JP2001177182A - External resonator semiconductor laser and optical waveguide device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small external resonator semiconductor laser whose oscillation wavelength is variable, which is stimulated by a main resonator and an auxiliary resonator and which can control the phase of the standing waves. SOLUTION: The external resonator semiconductor laser by this invention is constituted in such a way that an external light reflection part 301 which can control the wavelength at which reflectance is made maximum and a connection optical waveguide 302 capable of controlling a refractive index are formed integrally so as to be continued and that the connection optical waveguide 302 is arranged to face the low-reflection end face 209 of a semiconductor optical amplifier 2. The low-reflection end face 209 is formed in such a way that a light confinement region 207 is cleansed so as to be tilted from a face perpendicular to the advancing direction of the light to be propagated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tunable semiconductor laser used in the fields of optical communication and optical information processing, and more particularly to an external resonator type semiconductor laser which oscillates by using a resonator structure and its use. The present invention relates to an optical waveguide device.

[0002]

2. Description of the Related Art In general, an ideal external cavity semiconductor laser oscillates in a single longitudinal mode, has a narrow wavelength spectrum line width of output light, and can change an oscillation wavelength in a wide range. It has excellent potential capability and can be used for light sources for ultra-high-speed and high-bandwidth optical communication, optical information processing using optical interference, optical measurement, and the like.

FIG. 28 is a diagram showing a basic configuration of a general external cavity semiconductor laser. In FIG. 28, 2 is a semiconductor optical amplifier, 4 is a laser beam, 5 is a lens, 30
1 is an external light reflection part. The semiconductor laser is formed with a stripe-shaped light confinement region 207 having two end faces 208 and 209, one of which has a high reflectivity on the end face 208 side and a low reflectivity on the other end face 209.

In such a semiconductor laser, a laser resonator Mc is formed by an end face 208 of the semiconductor optical amplifier 2 having a higher reflectivity (hereinafter, referred to as a high reflection end face) and an external reflection means 301 (hereinafter, FIG. A laser resonator described as Mc in 28 is referred to as a main resonator). The low reflection end face 20
In the case where the reflection at 9 remains, a sub-resonator (referred to as _{Sc1 in} FIG. 28, hereinafter referred to as a first sub-resonator, and a longitudinal mode excited here) is formed by both end faces of the semiconductor optical amplifier. Is called an internal resonance mode), and the external light reflecting portion 301 and the low-reflection end surface 209 also form a sub-resonator (referred to as _{Sc2 in} FIG. 28, hereinafter, referred to as a second sub-resonator). The longitudinal mode excited here is called an external resonance mode). When only the main resonator is formed, the laser oscillates when the standing wave is excited in the main resonator, and when the sub-resonator is formed, the laser oscillates with the standing wave excited in the main resonator. Laser oscillation occurs when the phases of the standing waves excited in the sub-resonator coincide.

FIG. 29 is a diagram showing a resonator configuration and a standing wave phase relationship when no sub-resonator is present.
(A) shows the configuration of the resonator, and (b) shows the state of the standing wave at that time. However, this state occurs when the reflectance of the low reflection end face is sufficiently small.

[0006] As shown in FIG.
When only the main resonator 08 and the external light reflector 301 exist, the standing wave 4a is excited in the main resonator as shown in FIG. At this time, the phase of the standing wave on the low reflection end surface 209 is arbitrary.

FIG. 30 is a diagram showing the configuration of a resonator and the phase relationship of a standing wave when a sub-resonator is present.
(A) shows the configuration of the resonator when the first sub-resonator S _c1 and the second clothing resonator S _c2 exist, and (b) shows the state of the standing wave at that time. It is.

In this case, as shown in FIG. 30B, laser oscillation occurs only when the low reflection end face 209 and the node of the standing wave coincide. In the following description, setting the phases of the main resonator, the first sub-resonator, and the second sub-resonator to a state in which laser oscillation can be performed is referred to as “phase matching”, and the phases are matched. Phase control for phase adjustment
I will say that.

Next, a semiconductor optical amplifier used in a general external cavity semiconductor laser as described above will be described. FIGS. 31A and 31B are diagrams showing a main part configuration and a refractive index distribution of a conventional semiconductor optical amplifier, wherein FIG. 31A is a plan view of the main part structure, and FIG. In the drawing, (c) shows the refractive index distribution along XX of (a), and (d) shows the refractive index distribution along YY of (b).

In a conventional semiconductor optical amplifier, as shown in FIG. 31B, a first conductivity type semiconductor layer 202 and a semiconductor layer serving as an active layer (hereinafter, referred to as an active layer) are provided on a semiconductor substrate 201.
The structure is such that a semiconductor layer 203 and a second conductivity type semiconductor layer 204 are stacked. As shown in FIG. 31D, the active layer 20
3 has a relatively low bandgap energy and a high refractive index compared to the layers above and below, so that light is confined in the active layer in a direction perpendicular to the substrate surface. In the following description, such a structure is referred to as a double hetero pn junction structure. On the other hand, in the direction parallel to the surface of the semiconductor substrate 201, the layer structure is changed to locally form a high-refractive-index stripe (the local high-refractive-index stripe becomes the light confinement region 207). Light is confined in a direction parallel to the surface of the semiconductor substrate 201.

Here, considering the conditions that the low-reflection end face 209 should have, the essential requirement is not only that the reflectivity is low, but also that the light reflected by this end face should be confined to the light confinement region 207. Is low. Therefore, in the following description, the term "low reflectivity" includes "low reflectivity of the end face" and "low coupling efficiency of light reflected by the end face to the light confinement region 207", The end face having a low reflectance is referred to as a “low reflection end face”.

The external resonator type semiconductor laser having the above-mentioned configuration has heretofore been characterized by unity of oscillation longitudinal mode (less unnecessary harmonic components) and narrow line width of output light spectrum (color). (Purity), stability of optical output, expansion of wavelength variable width, and the like.

[0013] To achieve these objects, conventional, with reduced residual reflection of the low reflective facet 209, excited by the first sub-resonator S _c1 formed by both end faces 208 and 209 of the semiconductor optical amplifier 2 Phase of the standing wave excited by the second sub-resonator _Sc2 formed by the external light reflecting portion 301 and the low reflection end face 209, and the phase of the standing wave of the main resonator. Development of a phase control technique for matching each phase has been advanced.

As a conventional technique for reducing the residual reflection of the low reflection end face 209, for example, a technique in which a dielectric thin film is applied to the end face to reduce the reflectance is disclosed in JP-A-53-5798.
No. 5 (conventional example 1) and JP-A-59-145588 (conventional example 2). Further, for example, a technique for inclining a light confinement region and an intersection angle of an end face from a vertical direction is disclosed in JP-A-53-95589 (conventional example 3), JP-A-59-181588 (conventional example 4),
It is described in JP-A-10-12959 (conventional example 5) and the like. Further, for example, Japanese Patent Application Laid-Open No. 61-96787 (conventional example 6) and Japanese Patent Application Laid-Open No. 62-155582 (conventional example 7) disclose a technique of forming an end portion of a light confining region into a window structure. I have.

As a conventional technique for phase control for matching the phases of the respective standing waves, for example, a phase adjustment region is formed in a part of the optical confinement region of a semiconductor optical amplifier.
Methods for adjusting the phase of the standing wave excited in the first sub-resonator are described in Japanese Patent Application Laid-Open Nos. H1-224485 (Conventional Example 8) and Japanese Patent Application Laid-Open No. H7-335965 (Conventional Example 9). ing. Further, for example, as a method of adjusting the phase of a standing wave excited in the second sub-resonator, a method of disposing a bulk type phase adjusting means such as a crystal having an electro-optic effect in an external resonator is particularly preferable. JP-A-11-163469 (conventional example 1)
Japanese Patent Application Laid-Open No. 59-98579 (prior art 11) and the like, which adjust the position of a mirror which is an external light reflecting means, are described in JP-A-59-98579.

[0016]

However, the above conventional techniques have the following problems. When the conventional examples 1 to 7 are used for forming the low reflection end face 209, the reflection of the low reflection end face 209 remains. Therefore, for stable single mode oscillation, the first resonator S _c1
The phase of both the standing wave 41a excited in the second resonator S _c2 and the standing wave 41a excited in the second
08, the low-reflection end face 209, and the reflection surface of the external light reflection portion 301 must be adjusted to be located at the nodes of the standing waves 4a, 41a, and 42a. When performing these phase adjustments, the second resonator S _c2 is used only in the conventional examples 8 and 9.
Cannot be adjusted, so that the conventional example 10 or the conventional example 1
One needs to be combined.

However, when bulk type phase adjusting means such as a crystal having an electro-optical effect is used externally (conventional example 10)
There is a problem that the size of the semiconductor laser is increased both in the case where the mirror serving as the external light reflecting portion is moved (conventional example 11). In particular, when a lens or the like is required for optical coupling, there is a disadvantage that the size is further increased and the stability of optical coupling is deteriorated (problem 1).

In the case of the eleventh conventional example, it is necessary to control the position of the mirror which is the external light reflecting portion with an accuracy much shorter than the wavelength, and there is a problem that such position control is very difficult. (Issue 2).

Further, in Conventional Example 3 or Conventional Example 4, since both end faces of the semiconductor optical amplifier 2 are inclined, an end face corresponding to the high reflection end face 208 of Conventional Example 1 or Conventional Example 2 is formed. There is a problem that another external light reflecting portion is required. (Problem 3) In addition, in the conventional example 5, since the low-reflection end face 209 is formed by etching, it takes time to form the end face, and the end face becomes rough, so that the scattering loss tends to increase. (Issue 4).

An object of the present invention is to provide an external resonator type semiconductor laser which solves the above problems 1 to 4 simultaneously and an optical waveguide device used for the same.

[0021]

In order to achieve the above object, an external cavity semiconductor laser of the present invention has a core having a relatively high refractive index surrounded by a clad having a relatively low refractive index. An external light reflecting means having an optical waveguide, having a maximum reflectance for light of a specific wavelength, and capable of adjusting a wavelength at which the reflectance is maximum, and a first conductive material having a relatively large band gap. A semiconductor layer, an active layer that is a relatively small bandgap semiconductor layer and a relatively large bandgap second conductivity type semiconductor layer, having a stripe-shaped double hetero pn junction laminated on a semiconductor substrate, A light confinement region in which the refractive index of a portion defined as the stripe has a relatively higher refractive index than that of the outside of the stripe, and in which light propagates along the stripe; A high-reflection end face formed by cleaving the semiconductor substrate on a plane perpendicular to the traveling direction of light propagating through the region, and opposite to the high-reflection end face; Injecting a current into a low-reflection end face formed by cleaving the semiconductor substrate and a double hetero pn junction in the light confinement region on a surface inclined from a plane perpendicular to the traveling direction of light propagating in the region. And a semiconductor light amplifying means including: an optical waveguide of the external light reflecting means and a semiconductor light amplifying means disposed between the external light reflecting means and the low reflection end face of the semiconductor light amplifying means. The optical confinement region is optically coupled to the optical waveguide, and the optical waveguide continuously formed integrally with the external light reflecting means, and at least a part of the optical waveguide can change a refractive index with respect to propagating light. Refractive index available And parts, and the connection optical waveguide means that comprise, but be configured with.

In such a configuration, a laser resonator is formed by the high reflection end face of the semiconductor light amplification means and the external light reflection means, and laser oscillation occurs. Further, since the external light reflecting means can adjust the wavelength at which the reflectance becomes maximum, the laser oscillation wavelength becomes variable. Furthermore, the connecting optical waveguide means can change the refractive index of the optical waveguide with respect to the propagating light by the variable refractive index part, so that the distance between the semiconductor optical amplifier and the external light reflecting means can be substantially changed. become. As a result, it becomes possible to control and adjust the phase of the standing wave excited between the low reflection end face of the semiconductor optical amplification means and the external light reflection means.

In the above external cavity type semiconductor laser, the external light reflecting means, the semiconductor light amplifying means and the connecting optical waveguide means are respectively mounted on a common substrate and optically coupled. It may be.

In this configuration, the external light reflecting means, the semiconductor light amplifying means, and the connecting optical waveguide means are mounted on a common substrate and optical coupling is achieved, so that the semiconductor laser can be downsized. At the same time, the optical coupling becomes stable.

Further, in the above-described external cavity semiconductor laser, the connection optical waveguide means is formed by using the material whose refractive index with respect to propagating light changes according to temperature, and wherein the refractive index variable section is formed. However, a temperature controller that can adjust the temperature of the optical waveguide may be provided.

In such a configuration, by adjusting the temperature of the optical waveguide by the temperature adjuster, the refractive index with respect to the propagating light changes, and the constant light excited between the low reflection end face of the semiconductor optical amplifier and the external light reflection means. The phase of the standing wave can be controlled and adjusted. In such a configuration, the phase adjustment of the standing wave can be performed without a mechanical driving unit.

Alternatively, the connecting optical waveguide means may be arranged such that the optical waveguide surrounds a core having a relatively high refractive index with a clad having a relatively low refractive index and is coaxially arranged inside the core. An inner core having an electro-optic effect, wherein the variable refractive index portion includes an electrode for applying an electric field to the inner core of the optical waveguide.

In such a configuration, the refractive index of the inner core changes due to the electro-optic effect according to the electric field applied from the electrode, and the standing wave excited between the low reflection end face of the semiconductor optical amplifier and the external light reflection means. Can be controlled and adjusted. As a result, a higher-speed response can be achieved as compared with the case where the refractive index is controlled by adjusting the temperature of the optical waveguide, and the power consumption can be reduced.

In the above-described external cavity semiconductor laser, the external light reflecting means may be configured such that the optical waveguide has a refractive index with respect to propagating light that changes periodically along a traveling direction of the light, May be provided with a temperature adjuster capable of adjusting the temperature of.

In such a configuration, the optical waveguide configured so that the refractive index changes periodically along the traveling direction of light is:
The distributed reflection mirror has a maximum reflectance for light of a specific wavelength. Also, by adjusting the temperature of the optical waveguide by the temperature controller, the refractive index of the optical waveguide changes,
The wavelength at which the reflectance is maximized also changes.

Alternatively, in the external light reflecting means, the optical waveguide is disposed coaxially inside the core, has an electro-optic effect, and has a refractive index for propagating light along a traveling direction of light. An inner core that changes periodically may be provided, and an electrode for applying an electric field to the inner core may be provided.

In such a configuration, the inner core having an electro-optic effect and having a refractive index that periodically changes along the traveling direction of light becomes a distributed reflection mirror that has a maximum reflectance for light of a specific wavelength. . In addition, since the refractive index of the inner core changes due to the electro-optic effect according to the electric field provided by the electrode, the wavelength at which the reflectance becomes maximum also changes. As a result, a higher-speed response can be achieved as compared with the case where the refractive index is controlled by adjusting the temperature of the optical waveguide, and the power consumption can be reduced.

Further, it has a Mach-Zehnder type core structure connected to the optical waveguide of the external light reflecting means, one path is branched into two paths, and then merges into one path again. A portion branched into at least two paths, including an inner core having an electro-optical effect disposed coaxially with the core, and including an external light modulation unit having an electrode for applying an electric field to the inner core. May be configured.

In this configuration, the laser light output from the external light reflecting means is externally modulated by the Mach-Zehnder type external light modulating means. This eliminates the need to apply modulation to the semiconductor optical amplifier, and stabilizes laser oscillation. Further, since the external light modulating means is of the type using the electro-optical effect, high-speed modulation is possible and chirping of the modulated light is reduced.

In the above-described external cavity semiconductor laser, the semiconductor optical amplifier may have a portion in which the thickness of the active layer gradually decreases toward the low reflection end. . Further, the semiconductor optical amplifier may have a portion where the stripe width of the active layer gradually increases toward the low reflection end face. In addition, it is preferable that the semiconductor optical amplifier has a portion where at least one of the thickness and the stripe width of the active layer is constant including a portion in contact with the low reflection end face.

With this configuration, the reflectance at the low reflection end face can be further reduced. The external cavity semiconductor laser as described above can be specifically used as a plurality of light sources constituting an optical circuit device.

In one embodiment of the optical waveguide device according to the present invention, a core having a relatively high refractive index is surrounded by a clad having a relatively low refractive index, and is arranged coaxially inside the core. The optical waveguide includes an optical waveguide having an inner core having an electro-optic effect, and electrodes for applying an electric field to the inner core of the optical waveguide.

In such a configuration, the refractive index of the inner core changes due to the electro-optic effect according to the electric field applied from the electrode, and the phase and the like of the propagating light can be controlled and adjusted at high speed.

Another embodiment of the optical waveguide device according to the present invention has a Mach-Zehnder type core structure in which one path branches into two paths and then merges into one path again.
And an optical waveguide having an inner core having an electro-optic effect disposed coaxially with the core, and applying an electric field to the inner core of the optical waveguide for a portion of the core branched into at least two paths. And an electrode for the same.

With this configuration, an optical waveguide device that functions as a Mach-Zehnder type optical modulator that responds at high speed by utilizing the electro-optic effect is realized.

[0041]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing the configuration of the external cavity semiconductor laser of the first embodiment. FIG.
FIG. 2 is a cross-sectional view taken along a central axis of a light confinement region in which light propagates in FIG.

Referring to FIGS. 1 and 2, the external cavity semiconductor laser comprises a polyimide core 312 having a lower refractive index than a polyimide clad 311 on a common substrate 1 such as a silicon substrate. , 313 are formed, and a semiconductor optical amplifier 2 as a semiconductor optical amplifier is mounted on a portion 11 where the surface of the common substrate 1 is exposed.

The semiconductor optical amplifier 2 includes an n-type InP substrate 20
1 with respect to the first conductivity type semiconductor layer 2 which is an n-type InP layer
02, a double hetero-pn layer in which a multiple quantum well active layer 203 and a second conductivity type semiconductor layer 204 which is a p-type InP layer are stacked.
It is a joint structure. Since the substrate 201 is an n-type InP layer, the first conductivity type semiconductor layer 202 of the same n-type InP layer
May be omitted.

The active layer 203 has a layer structure and band gap energy as shown in an enlarged view of FIG. 3, for example. Specifically, a guide layer 230g having a relatively low bandgap energy is formed in contact with each of the first conductivity type semiconductor layer 202 and the second conductivity type semiconductor layer 204 having a high bandgap energy, and the guide layers 230g are formed. Between 230 g, the barrier layer 203 of a multiple quantum well having a lower band gap energy
b and the well layer 203w are formed alternately. Table 1 below shows a specific example of each layer.

[0045]

[Table 1]

The semiconductor optical amplifier 2 has, for example, 3 degrees (α = 3 degrees) with respect to the high reflection surface 208 formed by cleavage and the propagation axis of light propagating through the light confining region 207 on the high reflection surface 208 side. Degree) The light confinement region 20 is inclined.
7 is extended, and has a low-reflection end face 209 formed by cleavage at its tip. Light confinement region 207
Is 1.5 μm in a narrow portion, for example, and extends to 6.5 μm toward the low reflection end face 209. The thickness of the light confinement region 207 is reduced to, for example, 25% toward the low reflection end face. However, the width and the thickness near the low reflection end face 209 are constant. FIG. 4 (a)
(B) and (c) show AA, BB and C in FIG.
FIG. 4 is a diagram illustrating an example of a cross section cut along a line -C,
The part where 03 exists forms the light confinement region 207. The specific features of the structure near the low reflection end face 209 will be described later.

The planar optical waveguide 3 includes, for example, a core 312
The refractive index difference between the core 312 and the claddings 311 and 313 is about 0.4%, and the cross section of the core 312 is a rectangle of 7 μm × 7 μm or the like. On the surface above the core 312 of the planar optical waveguide 3,
A chromium thin film is deposited, which constitutes a first electric heater (first electrode) 304 and a second electric heater (second electrode) 305 as temperature controllers. The first electric heater 304 and the planar optical waveguide 3 located below the first electric heater 304 form a connecting optical waveguide 302 as connecting optical waveguide means, and the second electric heater 305 and the planar optical waveguide 3 located below the same. The wave path 3 forms an external light reflecting portion 301 as external light reflecting means.

FIGS. 5A and 5B are diagrams showing a specific configuration example of the external light reflecting portion 301, wherein FIG. 5A is a plan view, and FIG.
Is a cross-sectional view taken along the line Z-Z in FIG.
(C) is sectional drawing cut | disconnected along XX of (a).

As shown in FIGS. 5A to 5C, the core 312 of the planar optical waveguide 3 located at the external light reflecting portion 301
Is designed in advance so that the thickness of the light-emitting element periodically changes along the traveling direction of light. Specifically, the thickness of the core 312 is
For example, the thick part can be 7 μm, the thin part can be 6 μm, and the distance between the peaks can be 0.5 μm. With the core 312 having such a shape, the refractive index of the optical waveguide 3 becomes:
The thick part of the core 312 has a relatively high refractive index and the core 31
The thin portion 2 has a relatively low refractive index. Therefore, a so-called distributed reflection mirror is formed in which the refractive index of the optical waveguide 3 located in the external light reflecting portion 301 changes periodically along the traveling direction of light, and the reflectance for light of a specific wavelength becomes maximum. (Hereinafter, the wavelength at which the reflectance is maximized is referred to as the Bragg wavelength). The core 312, whose thickness changes periodically,
For example, using a known process such as exposing to ultraviolet light via a photomask, or performing two-beam interference exposure using ultraviolet light, or forming a mask pattern by direct drawing of an electron beam and then etching, Can be manufactured.

Here, the case where the core 312 and the clads 311 and 313 constituting the planar optical waveguide 3 are formed using an organic material such as polyimide has been described.
The core 312 and the claddings 311, 31 are not limited to this, and may be made of an organic-inorganic composite material such as polysiloxane.
3 may be formed.

In the above-described external cavity type semiconductor laser, a laser cavity is formed by the high reflection end face 208 and the external light reflection portion 301, and the laser oscillates. In addition, when a current is passed through the second electric heater 305 to heat the lower core 312, the Bragg wavelength shifts to the shorter wavelength side.
The oscillation wavelength shifts to the shorter wavelength side. Further, the optical waveguide 3
Since polyimide is used for the claddings 311 and 313 and the core 312, the change in the refractive index is large and the change in the oscillation wavelength is also large.

Also, by flowing a current through the first electric heater 304 to heat the connection optical waveguide 302, the refractive index of the connection optical waveguide 302 can be changed. The distance between the external light reflecting portions 301 can be changed. As a result, the second sub-resonator S between the low reflection end surface 209 and the external light reflection portion 301
The phase of the standing wave excited by _c2 can be controlled and adjusted.

More specifically, since the temperature coefficient of the refractive index of the optical material is generally as low as 1 × 10 ⁻⁵ / ° C. to 3 × 10 ⁻⁴ / ° C., fine phase adjustment is possible. For example, when the length of the region where the connection optical waveguide 302 is formed (hereinafter, referred to as a phase adjustment region) is 300 μm, the length change per 1 ° C. is 3 nm to 90 nm. Since it is easy to adjust the temperature with an accuracy of 0.1 ° C., it is possible to control the temperature with an accuracy of 0.3 nm to 9 nm. This accuracy is 1.3
The accuracy is sufficiently high for controlling the phase of light having a wavelength of μm to 1.5 μm.

Further, the active layer 203 of the semiconductor optical amplifier 2
Is reduced in thickness and widened toward the low reflection end face, so that the effect of reducing the reflectance of the low reflection end face can be obtained as described later. Thus, the bending angle α can be reduced, so that the semiconductor laser can be reduced in size. In addition, it is difficult to form a sub-resonator, so that the operation can be stabilized. Also, the external light reflecting portion 3
01 and the connection optical waveguide 302 are integrally formed continuously, so that the optical coupling state is stabilized.

In addition, the end surfaces 208,
209 from the viewpoint of manufacturability, each end face 208,
Since 209 is formed by cleavage, the end face can be easily formed and the scattering loss at the end face can be reduced. Also, since one end face of the semiconductor optical amplifier 2 is perpendicular to the light confinement region 207, this end face 208 can be made a high reflection end face, and other external light reflection means and the like are unnecessary as in the conventional case. become.

Here, the low reflection end face 2 of the semiconductor optical amplifier 2
The features of the structure near 09 (see FIGS. 1, 2 and 4) will be described step by step. First, a feature of the structure in which the thickness of the stripe-shaped light confinement region 207 (active layer 203) gradually decreases toward the low reflection end surface 209 will be described.

FIG. 6 is a view showing a structure in the case where the thickness of the active layer 203 is gradually reduced toward the low reflection end face (however, the width of the active layer 203 is fixed).
(A) is a plan view, (b) is a cross-sectional view cut along the central axis of the light confinement region, and (c) is A in (a).
It is sectional drawing cut | disconnected along -A.

As shown in FIG. 6, when the active layer 203 is gradually thinned toward the low reflection end face 209, the low reflection end face 2
09, the ability of the active layer 203 to confine the light decreases, and the spot size of the guided light beam increases. When the spot size increases, the light reflected on the inclined end surface 209 and the light confinement region 207
And the coupling efficiency decreases.

FIG. 7 is a diagram showing an example of calculating the coupling strength of the reflected light according to the difference in the shape of the active layer 203. The calculation in FIG. 7 is based on the document “D. Marcuse, JOURNAL OF LIG”.
HTWAVE TECHNOLOGY, VOL.7, No.2, pp.336-339 (1989) ''
And the layer structure shown in FIG. 3 and the structural parameters shown in Table 1 were used.

FIG. 7A shows that the stripe width of the active layer 203 is 1.5 μm and the active layer is InGaAsP / InGaAs.
It shows the relationship between the end face inclination angle and the coupling strength of reflected light when the thickness of the active layer 203 is constant without changing in the sP-based multiple quantum well structure. FIG. 7B shows the active layer 20.
3 has a stripe width of 1.5 μm and an active layer of InGaAs.
This graph shows the relationship between the end face inclination angle and the coupling strength of reflected light when the thickness of the active layer is reduced to 36% in a P / InGaAsP-based multiple quantum well structure. FIG. 7 (c)
Shows the relationship between the end face inclination angle and the coupling strength of reflected light when the stripe width of the active layer 203 described later is gradually increased.

7 (a) and 7 (b), for example, comparing the angles at which the coupling strength of the reflected light becomes -40 dB, the required inclination angle becomes approximately 11 by making the active layer thinner.
It can be seen that the temperature decreases from about 7 degrees to about 7 degrees. in this way,
By gradually reducing the thickness of the active layer 203, the coupling efficiency of the light reflected at the end face to the semiconductor optical waveguide decreases, so that the reflectivity at the low reflection end face 209 can be further reduced.

Further, a feature of the structure in which the thickness of the active layer 203 is constant near the low reflection end face 209 will be described. FIG. 8 is a cross-section taken along the central axis of the light confinement region when the thickness of the active layer 203 is constant near the low reflection end face 209 (however, the width of the active layer 203 is constant). FIG.

As shown in FIG. 8, the active layer 203 has a portion 21 whose thickness gradually decreases toward the low reflection end face 209.
3 and a portion 215 having a constant thickness including a portion in contact with the low reflection end face 209. In the active layer 203 having such a shape, the guided mode and the radiation mode easily interfere with each other at the portion 213 where the thickness changes. For example, in the case of the structure shown in FIG.
In some cases, interference occurs around 09 and the electric field intensity distribution oscillates. This phenomenon becomes more remarkable as the change in the thickness of the active layer 203 becomes steeper. When the electric field intensity distribution oscillates, the light intensity coupled to the connection optical waveguide 302 and the external light reflecting portion 301 also oscillates, and the characteristics of the laser become unstable.

Therefore, as shown in FIG.
If a portion 215 having a constant thickness is formed at the tip portion of the third light-contacting end surface 209 in contact with the low-reflection end surface 209, the radiation mode disappears as light propagates through this portion 215, so that interference hardly occurs. Thereby, the electric field distribution of the waveguide mode near the low reflection end face 209 becomes stable, and as a result, the effect of stabilizing the characteristics of the laser is obtained.

Next, the feature of the structure in which the stripe width of the active layer 203 gradually increases toward the low reflection end face 209 will be described. FIGS. 9A and 9B are diagrams showing a structure in which the stripe width of the active layer 203 is gradually widened toward the low reflection end face. FIG. 9A is a plan view, and FIG. 9B is a central axis of the light confinement region. It is sectional drawing cut | disconnected along. The figure shows a case where the thickness of the active layer 203 gradually decreases toward the low reflection end surface 209 and becomes constant near the low reflection end surface 209 as described above.

As shown in FIG. 9, the active layer 203 gradually decreases in thickness toward the low-reflection end face 209,
It has a portion 214 in which the stripe width gradually increases, and a portion 215 in which the thickness and width are constant including a portion in contact with the low reflection end surface 209.

In a region where the thickness of the active layer 203 is relatively thick (region where z = 0 to z = z3), it is necessary to make the stripe width relatively narrow in order to guide only the fundamental mode. However, as described above, when the thickness of the active layer 203 is gradually reduced, the maximum stripe width capable of maintaining a single mode is increased. Therefore, in the portion 214 where the thickness of the active layer 203 is reduced, the stripe width is gradually increased within a range where a single mode can be maintained, and the width of the guided mode (stripe width) is increased. 2
The light coupling efficiency between the light reflected at 09 and the light confinement region 207 is reduced, so that the low reflection end face 209 is further reduced in reflection.

Specifically, the coupling strength of the reflected light as shown in FIG. 7C is calculated. However, FIG.
(C) shows that the active layer is made of InGaAsP / InGaAsP.
In the system multiple quantum well structure, when the stripe width is widened to 6.5 μm and the thickness of the active layer is reduced to 25% on the low reflection end face 209, the relationship between the end face inclination angle and the coupling strength of reflected light is shown. Is shown. For example, comparing the angle at which the coupling intensity of the reflected light becomes −40 dB in FIGS. 7B and 7C, the required inclination angle is increased from about 7 degrees to about 3 degrees by increasing the stripe width. It can be seen that it is reduced.

Further, here, by providing the portion 215 where the thickness and width of the active layer 203 are constant near the low reflection end face 209, the interference between the guided mode and the radiation mode is reduced as described above. As a result, a low-reflection end face 209 having a lower reflectance is realized.

In the first embodiment described above, the portion 303 where the thickness of the core 312 changes periodically is formed as the external light reflecting portion 301, but the present invention is not limited to this. is not. Hereinafter, the external light reflecting portion 30
An example of the structure of an optical waveguide applicable as 1 is listed.

FIGS. 10A and 10B show an example in which the refractive index of the planar optical waveguide 3 located at the external light reflecting portion 301 is periodically changed. FIG. 10A is a plan view, and FIG. )
(A) is a refractive index distribution of the optical waveguide 3 along Z-Z of (a), and (c) is a cross-sectional view cut along XX of (a).

As shown in FIGS. 10A to 10C, the refractive index of the portion 303 of the optical waveguide including the core 312 and the claddings 311 and 313 around the core 312 periodically changes along the light traveling direction. A distributed reflection mirror that is pre-designed to vary and has a Bragg wavelength is formed. Above the portion 303 where the refractive index changes periodically, a second electric heater 305 is provided. When the temperature of the optical waveguide changes according to the heating by the electric heater 305, the refractive index also changes. . If the refractive index of the entire optical waveguide changes, the Bragg wavelength of the distributed reflection mirror changes, and the wavelength at which the reflectance becomes maximum also changes. Therefore, the oscillation wavelength of the external resonator type semiconductor laser can be changed by using the above-described optical waveguide as the external light reflecting portion 301.

FIGS. 11A and 11B show an example in which the refractive index of the core 312 located at the external light reflecting portion 301 changes periodically. FIG. 11A is a plan view, and FIG. FIG. 3A is a cross-sectional view of the refractive index distribution of the optical waveguide 3 along ZZ, and FIG. 3C is a cross-sectional view taken along XX of FIG.

As shown in FIGS. 11A to 11C, the core 31 of the planar optical waveguide 3 located at the external light reflecting portion 301
2 is designed in advance so that the refractive index changes periodically along the traveling direction of light, and a distributed reflection mirror is formed in the same manner as in the case shown in FIG. A second electric heater 305 is provided above the core 312 whose refractive index changes periodically.
, The refractive index of the optical waveguide changes, and the Bragg wavelength of the distributed reflection mirror changes. Therefore, by using such an optical waveguide as the external light reflecting portion 301, the oscillation wavelength of the external resonator type semiconductor laser can be changed.

In order to form the core 312 whose refractive index changes periodically as described above, for example, a high energy ray such as an ultraviolet ray or an electron beam may be applied to a portion where the refractive index is to be increased. Specifically, in the case of ultraviolet rays, a desired refractive index distribution can be imparted by exposure through a photomask or by two-beam interference exposure. In the case of an electron beam, a desired refractive index distribution can be provided by direct writing.

FIGS. 12A and 12B show an example in which the width of the core 312 located at the external light reflecting portion 301 is changed periodically. FIG. 12A is a plan view, and FIG. 3) is a cross-sectional view taken along the line Z-Z of FIG.
It is sectional drawing cut | disconnected along XX of FIG.

As shown in FIGS. 12A to 12C, the core 31 of the planar optical waveguide 3 located at the external light reflecting portion 301
2 is designed in advance so that it changes periodically along the light traveling direction. For example, the width of the core 312 may be 7.5 μm at a wide portion, 6 μm at a narrow portion, and the thickness of the core may be 6 μm. With the core 312 having such a shape, the refractive index of the optical waveguide 3 is relatively high in a portion where the width of the core 312 is wide, and relatively low in a portion where the width of the core 312 is narrow. Therefore, the refractive index of the optical waveguide 3 located in the external light reflecting portion 301 changes periodically along the traveling direction of light, and a distributed reflection mirror having a Bragg wavelength is formed. Further, a second electric heater 305 is provided above the core 312 whose width periodically changes, and according to heating by the electric heater 305,
The refractive index of the optical waveguide 3 changes, and the Bragg wavelength of the distributed reflection mirror changes.

The core 31 whose width varies periodically
2 is, for example, exposed to ultraviolet light through a photomask,
Alternatively, two-beam interference exposure using ultraviolet light is performed, or a mask pattern is formed by direct drawing of an electron beam,
Then, using a known process such as etching,
It can be easily manufactured.

FIG. 13 shows an example in which strip-shaped portions 317 having different refractive indexes are periodically arranged in the core 312 located in the external light reflecting portion 301, and FIG. 13A is a plan view. (B) is a cross-sectional view taken along the line ZZ of (a), and (c) is a cross-sectional view taken along the line XX of (a).

As shown in FIGS. 13 (a) to 13 (c), the core 312 located in the external light reflecting portion 301
A strip-shaped portion 317 having a refractive index different from 2 (hereinafter referred to as a strip) is periodically arranged along the traveling direction of the propagating light. Specifically, the thickness and width of one strip of the strip portion 317 is 0.2 μm × 0.2 μm, and the pitch is 0.5 μm.
And so on. For example, when the refractive index of the strip 317 is higher than that of the core 312, the portion having the strip 317 has a relatively high refractive index, and the portion having no strip has a relatively low refractive index. Conversely, the strip 317 is the core 312
In the case where the refractive index is lower than that, a portion having a strip has a relatively low refractive index, and a portion having no strip 317 has a relatively high refractive index. Therefore, the refractive index of the optical waveguide 3 located in the external light reflecting portion 301 changes periodically along the traveling direction of light, and a distributed reflection mirror having a Bragg wavelength is formed. The core 312 on which the strips 317 are periodically arranged.
A second electric heater 305 is provided above the optical waveguide 3. The refractive index of the optical waveguide 3 changes according to the heating by the electric heater 305, and the Bragg wavelength of the distributed reflection mirror changes. The core 312 on which the strips 317 are arranged as described above is exposed to ultraviolet rays through a photomask, or is subjected to two-beam interference exposure using ultraviolet rays, for example.
Alternatively, it can be easily manufactured by using a known process such as forming a mask pattern by direct drawing of an electron beam and then etching.

FIG. 14 shows a strip-shaped portion 31 having a different refractive index in the cladding 313 located at the external light reflecting portion 301.
8A is a plan view, FIG. 8B is a cross-sectional view taken along the line Z-Z of FIG. 7A, and FIG. 8C is a cross-sectional view of FIG. 3) is a cross-sectional view taken along XX of FIG.

As shown in FIGS. 14A to 14C, a strip 318 having a refractive index different from that of the clad 313 is provided along the traveling direction of the propagating light in the clad 313 located at the external light reflecting portion 301. Are arranged periodically. For example, strip 3
In the case where the refractive index of the strip 18 is higher than that of the cladding 313, the portion where the strip 317 is located has a relatively higher refractive index,
The portion without the strip 318 has a relatively low refractive index. Conversely, when the strip 318 has a lower refractive index than the cladding 313, a portion having the strip 318 has a relatively low refractive index, and a portion having no strip has a relatively high refractive index. Therefore, the refractive index of the optical waveguide 3 located in the external light reflecting portion 301 changes periodically along the traveling direction of light, and a distributed reflection mirror having a Bragg wavelength is formed. A second electric heater 305 is provided above the cladding 313 on which the strips 318 are periodically arranged.
5, the refractive index of the optical waveguide 3 changes,
The Bragg wavelength of the distributed reflection mirror changes. The core 313 on which the strips 318 are arranged as described above is also exposed to ultraviolet light through a photomask, for example, or
It can be easily manufactured by using a known process such as two-beam interference exposure using ultraviolet light, or forming a mask pattern by direct drawing of an electron beam and then etching.

Next, a second embodiment of the present invention will be described. FIG. 15 is a plan view showing the configuration of the external cavity semiconductor laser according to the second embodiment. FIG. 16 is the same as FIG.
FIG. 5 is a cross-sectional view taken along a center axis of a light confinement portion through which light propagates in FIG. However, the same parts as those in the configuration of the first embodiment are denoted by the same reference numerals, and the same applies to the following embodiments.

In FIGS. 15 and 16, the external cavity semiconductor laser according to the first embodiment has the same structure as that of the first embodiment described above, except that the inside of the core 312 of the planar optical waveguide 3 formed of, for example, a UV-curable epoxy resin. In addition, an inner core 314 made of an organic material having an electro-optical effect is formed (hereinafter, referred to as a double core structure).
The configuration of other parts other than the application of the double core structure is the same as the configuration of the first embodiment.

The inner core 314 is formed inside the core 312 located in the connecting optical waveguide 302 here.
The inner core 314 is connected to the first electrode 3 located above.
14 (corresponding to the first electric heater in the first embodiment)
Changes the refractive index according to the applied electric field. Thereby, the phase of the laser beam can be adjusted. Although the configuration in which the electrodes are formed only above the inner core 314 is shown here, the electrodes may be formed below the inner core 314.

FIG. 17 is a view specifically showing an example of the structure of the portion where the inner core 314 is formed.
Is a plan view, (b) is a ZZ sectional view in (a),
(C) is an X1-X1 cross-sectional view in (a), (d) is an X2-X2 cross-sectional view in (a), and (e) is an X3-X3 cross-sectional view in (a). In addition, Y1-Y1, Y2-Y2, and Y3-Y3 in FIG.
They correspond to X1-X1, X2-X2 and X3-X3 of (a), respectively.

As shown in FIG. 17A, the inner core 314 has a tapered shape in which both end portions 315 are gradually narrowed. However, as shown in FIG. 17B, the thickness of the inner core 314 is constant. That is, in the central portion of the inner core 314, as shown in FIG.
An inner core 314 having a cross-sectional shape similar to the cross-sectional shape of the core 312 is formed coaxially at the center of the core 312. The core 3 is located above the inner core 314.
The first electrode 304 is formed via the second electrode 12 and the clad 313. In the structure example shown in FIG. 17, the core 312 and the clad 3 are also provided below the inner core 314.
11 shows a case where the electrode 306 is formed via the electrode 11. The electrode 306 is formed at the boundary between the common substrate 1 and the clad 311, and a part thereof is formed on the clad 31 on the common substrate 1.
1. It is assumed that an electrode exposed portion 316 exposed outside is provided.

On the other hand, at both end portions of the inner core 314, as shown in FIG. 17D, the inner core 314 whose width (length in the horizontal direction in the figure) is gradually narrowed is reduced.
Are formed coaxially at the center portion of. Note that here, the first electrode 304 and the electrode 306 are
(See FIG. 17).
(See (a) and (b)). Further, in a portion outside the both ends of the inner core 314, as shown in FIG. 17E, the inner core 314 is eliminated, and the planar optical waveguide 3 having only the core 312 is formed.

In the above-described double-core structure, an optical waveguide having an electro-optical effect (hereinafter referred to as an active optical waveguide) used for the inner core 314 and another optical waveguide having no electro-optical effect used for the core 312 (hereinafter referred to as an active optical waveguide). Hereinafter, this is referred to as a passive optical waveguide). Thus, most of the planar optical waveguide 3 constituting the external light reflecting portion 301 and the connection optical waveguide 302 can be constituted by the passive waveguide, and the active waveguide can be incorporated in the main part. Propagation loss as a whole can be reduced. Further, the inner core 314
Is joined to the core 312 in a tapered shape at both ends, so that the coupling loss between the active optical waveguide and the passive optical waveguide can be reduced.

Therefore, according to the second embodiment, the refractive index of the connection optical waveguide 302 can be changed according to the electric field applied by the first electrode 314, so that the refractive index of the connection optical waveguide 302 changes according to the temperature change as in the first embodiment. Compared with the case where the refractive index is made variable, the phase adjustment of the laser beam can be performed at a higher speed. In addition, even if a material having an electro-optic effect is applied to the optical waveguide, the increase in propagation loss can be suppressed to a relatively small value due to the double core structure as described above.

The optical waveguide of the double core structure applied in the second embodiment is not limited to use as an optical waveguide of an external resonator type semiconductor laser, but also as an optical waveguide device used in various optical circuits. It can be widely applied. That is, the material having the electro-optic effect has a relatively large propagation loss as compared with other materials having no electro-optic effect. For this reason, when a large-scale optical circuit is formed by an optical waveguide having an electro-optic effect (active optical waveguide), the loss tends to increase. However, the optical waveguide device manufactured in the same manner as in the second embodiment can be monolithically integrated with the active optical waveguide and another optical waveguide having no electro-optic effect (passive optical waveguide). This is useful because the propagation loss is reduced.

FIG. 18 is a plan view showing an example of an optical waveguide device in which most of an optical circuit is constituted by passive waveguides and an active waveguide is incorporated in a main part. In FIG. 18, an active optical circuit section 320 is an optical circuit partially constituted by an active optical waveguide including an inner core 314.
340 is an optical circuit composed of a passive optical waveguide. The optical waveguide device having such a circuit configuration has a very small loss as compared with an optical circuit including only active optical waveguides.

Further, the optical waveguide having the double core structure may be applied to the external light reflecting portion 301. Hereinafter, a configuration example of an optical waveguide having a double-core structure applicable as the external light reflecting portion 301 will be described.

FIG. 19 shows an example in which an inner core 314 having a periodically changing refractive index is formed in a core 312 located in the external light reflecting portion 301. FIG. 19A is a plan view. (B) is an optical waveguide 3 along ZZ of (a).
(C) is a cross-sectional view taken along XX of (a).

As shown in FIGS. 19A to 19C, the inside of the core 312 located in the external light reflecting portion 301 has an electro-optic effect and has a refractive index along the traveling direction of the propagating light. The inner core 314 whose periodically changes
A distributed reflection mirror which is formed coaxially at the center of the mirror 12 and has a maximum reflectance for light of a specific wavelength is formed. Specifically, for example, the width at the central portion of the inner core 314 can be 2 μm and the thickness can be 1.5 μm. An electrode 304 and an electrode 306 are provided above and below the inner core 314 whose refractive index changes periodically.
When the refractive index of the inner core changes according to the electric field caused by the above, the period of the refractive index change (effective period) also changes.
The Bragg wavelength of the distributed mirror also changes. Therefore, by using such an optical waveguide as the external light reflecting portion 301, the oscillation wavelength of the external resonator type semiconductor laser can be changed.

In order to form the inner core 314 whose refractive index changes periodically as described above, for example, a high-energy ray such as an ultraviolet ray or an electron beam may be applied to a portion where the refractive index is to be increased. Specifically, in the case of ultraviolet rays, a desired refractive index distribution can be imparted by exposure through a photomask or by two-beam interference exposure. Also,
In the case of an electron beam, a desired refractive index distribution can be provided by direct writing.

FIG. 20 shows an example in which an inner core 314 whose thickness changes periodically is formed in a core 312 located at the external light reflecting portion 301. FIG. 20A is a plan view. (B) is a cross-sectional view cut along ZZ of (a), and (c) is a cross-sectional view cut along XX of (a).

As shown in FIGS. 20A to 20C, the inside of the core 312 located at the external light reflecting portion 301 has an electro-optic effect and has a thickness along the traveling direction of the propagating light. Is periodically changed, and the inner core 314
2 are formed coaxially at the center. Specifically, for example, the thickness of the inner core 314 ranges from a minimum of 1 μm to a maximum of 1.
It may be changed periodically in a range of 5 μm or the like. With such a double core structure, the inner core 3
The portion where the thickness is 14 has a relatively high refractive index, and the portion where the inner core 314 is thin has a relatively low refractive index. Therefore, the refractive index of the optical waveguide 3 located in the external light reflecting portion 301 changes periodically along the traveling direction of light, and a distributed reflection mirror having a Bragg wavelength is formed. An electrode 304 and an electrode 306 are provided above and below the inner core 314 whose thickness changes periodically. The refractive index of the inner core changes according to the electric field generated by the electrodes 304 and 306. , The Bragg wavelength of the distributed reflection mirror changes.

For example, the inner core 314 whose thickness changes periodically is exposed to ultraviolet light through a photomask, or subjected to two-beam interference exposure using ultraviolet light, or directly drawn with an electron beam. It can be easily manufactured using a known process such as forming a mask pattern and then etching.

FIG. 21 shows that the inner core 312 whose width is periodically changed is provided in the core 312 located at the external light reflecting portion 301.
FIG. 14A is a plan view, FIG. 14B is a cross-sectional view taken along the line Z-Z of FIG. 14A, and FIG. 14C is a cross-sectional view of FIG. It is sectional drawing cut | disconnected along -X.

As shown in FIGS. 21A to 21C, the core 312 located in the external light reflecting portion 301 has an electro-optic effect and has a width along the traveling direction of the propagating light. The periodically changing inner core 314 is
Are formed coaxially at the center portion of. With such a double core structure, a portion where the width of the inner core 314 is wide has a relatively high refractive index, and a portion where the width of the inner core 314 is narrow has a relatively low refractive index. Therefore, the refractive index of the optical waveguide 3 located in the external light reflecting portion 301 changes periodically along the traveling direction of light, and a distributed reflection mirror having a Bragg wavelength is formed. An electrode 304 and an electrode 306 are provided above and below the inner core 314 whose width changes periodically.
The refractive index of the inner core changes according to the electric field caused by
The Bragg wavelength of the distributed reflection mirror changes. Also for the inner core 314 whose width changes periodically,
As in the case where the thickness changes periodically, it can be easily manufactured using a known process.

Next, a third embodiment of the present invention will be described. FIG. 22 is a plan view showing a schematic configuration of the external cavity semiconductor laser of the third embodiment.

As shown in FIG. 22, the external cavity semiconductor laser according to the present embodiment is different from the first and second embodiments in that the external modulation as external light modulating means for modulating the emitted laser light. The device 320 is monolithically integrated outside the output side of the external light reflecting portion 301 of the planar optical waveguide 3. The configuration other than the provision of the external modulator 320 is the same as that of the first and second embodiments, and thus the description is omitted.

FIG. 23 is an enlarged view of a part of the external modulator 320. FIG. 23A is a plan view,
(B) is sectional drawing cut | disconnected along XX of (a). As shown in FIG. 23, in the external modulator 320, for example, a Mach-Zehnder optical modulator for performing light intensity modulation using an electro-optic effect is formed on the output side of the planar optical waveguide 3. Specifically, for the core 312a having one path extended from the external light reflecting portion 301,
A core 31 that branches into two paths and then merges again into one
2b and a core 312c extending as one path from the junction of the cores 312b are integrally formed continuously in this order. Further, the cores 312a, 312b, 31
2c has claddings 311, 31 having a lower refractive index than those.
3 constitutes a part of the planar optical waveguide 3.

A portion 312b of the cores 312a to 312c branched into at least two paths is provided with an inner core 314 made of a material having an electro-optic effect.
Are formed coaxially at the center of each path of the core 312b. The shape of the inner core 314 formed in each path is the same as that of the second embodiment described above.
15 has a tapered shape. Further, thin film electrodes 304 and 306 are provided above and below the portion where the inner core 314 is formed, and an electric field is applied to the inner core 314.

In the external modulator 320 configured as described above, in the core 312b branched into two paths, the refractive index of each path changes according to the electric field applied by the electrodes 304 and 306. , The phase of the laser light passing therethrough is controlled independently. As a result, the laser light output from the external light reflector 301 can be externally modulated, and the laser oscillation can be stabilized as compared with the case where the semiconductor optical amplifier 2 is directly modulated. Further, since the external modulator 320 is monolithically integrated in the planar optical waveguide 3, a small-sized semiconductor laser having a low-loss external modulation function can be realized. Further, since the external modulator 320 is of the type using the electro-optic effect, it is possible to perform high-speed modulation and to reduce the chirping of modulated light.

The Mach-Zehnder type optical modulator having the double core structure applied in the third embodiment is not limited to use as an external modulator of an external cavity type semiconductor laser, but may be applied to various optical circuits. It can be widely applied as an optical waveguide device used as a device.

Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, a specific application example using the external cavity semiconductor laser according to the first to third embodiments will be considered.

FIG. 24 is a plan view showing an example of an optical circuit device that uses an external cavity semiconductor laser according to the present invention as a light source and connects a plurality of terminals with a relatively simple configuration. The optical circuit device shown in FIG. 24 connects electronic circuits with each other. For example, an input side on which four 4 × 4 ATM switches (electric switches) 805 are arranged and four optical circuits are connected. And the output side on which four 4 × 4 ATM switches (electrical switches) 807 are arranged.
It is a configuration connected by. Such an optical circuit device has 16
It can be used as a ch.times.16 ch ATM packet switching device or an Internet router. The O / E 804 on the input side is a photoelectric converter, and the E / O 808 on the output side is an electro-optical converter.

More specifically, the plurality of external cavity semiconductor lasers 100 used as light sources are, for example, as shown in FIG.
Having a configuration similar to that shown in FIG.
_{0, λ 1 ..., λ C} , it is preset to the laser oscillation at lambda _F. In each of the external cavity semiconductor lasers 100, the planar optical waveguide 3 (see FIG. 1) constituting the external light reflecting portion 301 is extended, and a simple extension 701 is formed. Light intensity modulating means 801 is formed in the simple extension part 701 so as to correspond to each semiconductor laser 100, and each intensity light modulating means 801 is driven according to a signal sent from an input-side ATM switch 805. This light intensity modulation means 801
For example, SOA (Semiconductor Optical Am
plifier) gate or a Mach-Zehnder optical modulator as shown in FIG. 23 described above.

After passing through the simple extension part 701, the light modulating means 8
01 is modulated by the multiplexing unit 702 and the light is intensity-modulated by the multiplexing unit 702.
To be united. Then, the light of each wavelength that has passed through the binding unit 703 is branched by the branching unit 704, passes through the band-pass filter 802 inserted in the light path, and then passes through the O / E converter 803 including the photodiode. Is entered. For example, if the transmission wavelength of the band-pass filter is selected from the top in the figure as λ ₀ , λ ₄ , λ ₈ , λ _C , λ ₁ , λ ₅ ,... . As the bandpass filter 802, for example, a dielectric filter (individual bandpass filter) in which a dielectric film is laminated on a thin film substrate, or a λ / 4 shift type diffraction as shown in the cross-sectional view of FIG. For example, a band-pass filter including a grating 371 and a transmission wavelength adjusting heater 372 can be used.

The bandpass filter shown in FIG. 25 will be described in detail. The bandpass filter is, for example, a planar optical waveguide in which a polyimide core 312 is surrounded by polyimide claddings 311 and 313 on a silicon substrate 1. 3 is formed, and a λ / 4 shift type diffraction grating 371 having a concavo-convex shape having a center pitch of 258 μm and other portions having a pitch of about 516 nm is formed on the core 312, the transmission center wavelength is about 1.55 μm. Pass filter 802
become. Also, if a heater made of a chromium thin film is formed on the surface of the bandpass filter 802 to adjust the temperature, the transmission center wavelength of the filter can be adjusted. FIG. 25 shows a case where the waveguide type photodiode 9 is arranged to face the bandpass filter 802.

According to the optical circuit device having the above configuration,
Since the wavelength of the light source and the wavelength of the filter can be adjusted, arbitrary terminals can be connected one-to-one.
When the light source and the light receiving element are connected one-to-one with independent cores, the cores may need to cross each other. However, by using the optical wiring circuit 7 as described above, the optical wiring core patterns cross each other. Any terminal can be connected without the need. Eliminating the intersection of the cores has the effect of simplifying the optical wiring pattern and at the same time reducing the loss at the intersection and reducing crosstalk. In addition, since the optical wiring does not become a capacitive load like electric wiring, high-speed optical transmission becomes possible and power consumption can be reduced. Further, if a Mach-Zehnder type optical modulator as shown in FIG. 23 is used as the light intensity modulating means 801, the optical wiring circuit 7 and the optical modulation device are integrated, so that miniaturization and low loss can be realized. .

In the fourth embodiment, an array waveguide type diffraction grating can be used as the multiplexing means 702. FIG. 26 shows a configuration example of an optical circuit device using an arrayed waveguide type diffraction grating (AWG). When an arrayed waveguide type diffraction grating is used for the multiplexing means 702, an effect is produced that the loss of the multiplexing means 702 is reduced.

As an application example of the fourth embodiment, as shown in FIG. 27, a function of monitoring the wavelength of laser light may be provided. In the configuration example of FIG. 27, the binding unit 703 of the optical circuit device shown in FIG.
And a second array waveguide type diffraction grating (AWG) 708. By making the demultiplexing characteristics of the arrayed waveguide type diffraction grating 702 and the second arrayed waveguide type diffraction grating 708 the same, each output of the output port 709 of the second arrayed waveguide type diffraction grating 708 is maximized. By adjusting the oscillation wavelength of the external resonator type semiconductor laser as described above, the loss of the optical circuit device is minimized.

It is needless to say that the wavelength of each band-pass filter 802 is also adjusted so that the transmission loss of the light of the target wavelength is minimized. The optical circuit device shown in FIG. 26 is also not shown, but is connected to the binding unit 703 by the monitor branching unit 70 in the same manner as described above.
7 and the second arrayed waveguide grating 708 facilitate adjustment of the oscillation wavelength of each external cavity semiconductor laser 100.

[0117]

As described above, according to the present invention, the oscillation wavelength is variable, and at the same time, the phase of the standing wave excited between the low reflection end face of the semiconductor optical amplification means and the external light reflection means is controlled. The size of the adjustable external cavity semiconductor laser can be reduced, and the optical coupling state can be stabilized. Further, since the high-reflection end face and the low-reflection end face of the semiconductor optical amplifying means are formed by cleavage, the end face can be easily formed, and the scattering loss at the end face can be reduced. Further, since the refractive index of the optical waveguide is changed by using temperature adjustment or electro-optic effect, it is possible to adjust the oscillation wavelength and control the phase with high accuracy and at high speed.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of an external cavity semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along a central axis of a light confinement region in which light propagates in FIG.

FIG. 3 is a diagram illustrating a layer structure and band gap energy of an active layer according to the first embodiment.

FIG. 4 is a diagram showing an example of a cross section cut along AA, BB, and CC in FIG. 1;

FIG. 5 is a diagram illustrating a specific configuration example of an external light reflection unit according to the first embodiment.

FIG. 6 is a diagram illustrating characteristics of the shape of the active layer according to the first embodiment, and is a diagram illustrating a structure when the thickness is gradually reduced toward a low reflection end surface.

FIG. 7 is a diagram illustrating an example of calculating a coupling strength of reflected light according to a difference in the shape of an active layer according to the first embodiment.

FIG. 8 is a diagram illustrating characteristics of the shape of the active layer according to the first embodiment, and is a diagram illustrating a structure when the thickness is constant near a low reflection end surface.

FIG. 9 is a diagram illustrating characteristics of the shape of the active layer according to the first embodiment, and is a diagram illustrating a structure in which the stripe width of the active layer is gradually increased toward a low reflection end surface.

FIG. 10 is a diagram illustrating another configuration of the external light reflecting portion related to the first embodiment, and is a diagram illustrating an example in which the refractive index of the planar optical waveguide is periodically changed. .

FIG. 11 is a diagram showing another configuration of the external light reflecting portion related to the first embodiment, and is a diagram showing an example in which the refractive index of the core is changed periodically.

FIG. 12 is a diagram illustrating another configuration of the external light reflecting portion related to the first embodiment, and is a diagram illustrating an example in a case where the width of a core is periodically changed.

FIG. 13 is a diagram illustrating another configuration of the external light reflecting portion related to the first embodiment, and is a diagram illustrating an example in which strips having different refractive indexes are arranged in a core.

FIG. 14 is a diagram illustrating another configuration of the external light reflecting portion related to the first embodiment, and is a diagram illustrating an example in which strips having different refractive indexes are arranged in a clad.

FIG. 15 is a plan view showing a configuration of an external cavity semiconductor laser according to a second embodiment of the present invention.

FIG. 16 is a cross-sectional view taken along a central axis of a light confinement region where light propagates in FIG.

FIG. 17 is a diagram illustrating an example of a structure of a portion where an inner core is formed according to the second embodiment.

FIG. 18 is a plan view showing an example of an optical waveguide device in which a large part of an optical circuit is formed of a passive waveguide and an active waveguide is incorporated in a main part according to the second embodiment.

FIG. 19 is a diagram showing another configuration of the external light reflecting portion related to the second embodiment, and is an example in which an inner core whose refractive index changes periodically is formed in the core.

FIG. 20 is a diagram showing another configuration of the external light reflecting portion related to the second embodiment, and is an example in which an inner core having a thickness that changes periodically is formed in the core.

FIG. 21 is a view showing another configuration of the external light reflecting portion related to the second embodiment, and is an example of a case where an inner core whose width changes periodically is formed in the core.

FIG. 22 is a plan view showing a schematic configuration of an external cavity semiconductor laser according to a third embodiment of the present invention.

FIG. 23 is an enlarged view of an external modulator according to the third embodiment.

FIG. 24 is a plan view showing an example of an optical circuit device for connecting a plurality of terminals using an external cavity semiconductor laser according to the present invention as a light source.

25 is a sectional view showing an example of a bandpass filter used in the optical circuit device shown in FIG.

26 is a plan view showing an example of the optical circuit device of FIG. 24 when an arrayed waveguide type diffraction grating is used as a multiplexing means.

FIG. 27 is a plan view showing an example of a case where the optical circuit device of FIG. 26 has a function of monitoring a laser light wavelength.

FIG. 28 is a diagram showing a basic configuration of a general external cavity semiconductor laser.

FIG. 29 is a diagram illustrating a configuration of a resonator and a phase relationship of a standing wave when a sub-resonator is not present.

FIG. 30 is a diagram illustrating a configuration of a resonator and a phase relationship of a standing wave when a sub-resonator is present.

FIG. 31 is a diagram showing a configuration of a main part of a conventional semiconductor optical amplifier and a refractive index distribution thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Common board | substrate 2 ... Semiconductor optical amplifier 201 ... Semiconductor substrate 202 ... First conductivity type semiconductor layer 203 ... Active layer 204 ... Second motor type semiconductor layer 205,206 ... Electrode 207 ... Light confinement area 208 ... High reflection end face 209 ... Low-reflection end face 3 Planar optical waveguide 301 External light reflecting section 302 Connection optical waveguide 304 First electric heater (first electrode) 305 Second electric heater (second electrode) 306 Electrode 311 ... clad 312 ... core 313 ... clad 314 ... inner core 317, 318 ... strip-shaped part 100 ... external resonator type semiconductor laser 7 ... optical wiring circuit 701 ... simple extension part 702 ... multiplexing means 703 ... binding part 704 ... branch Means 801: Light modulation means 802: Band pass filter

Continued on the front page F term (reference) 2H047 KA04 MA07 NA02 QA05 RA08 2H079 AA02 AA06 BA01 BA03 CA04 CA05 DA16 DA17 EA05 EA27 5F073 AA22 AA65 AA67 AA74 AA83 AA89 AB21 AB25 BA02 BA09 CA07 CA12 EA04 FA13 BA21 BA21

Claims (13)

[Claims] An optical waveguide having a relatively high refractive index core surrounded by a relatively low refractive index clad;
External light reflecting means whose reflectance is maximum for light of a specific wavelength, and which can adjust the wavelength at which the reflectance is maximum, a first conductivity type semiconductor layer having a relatively large band gap,
An active layer, which is a semiconductor layer having a relatively small bandgap, and a second conductivity type semiconductor layer, which has a relatively large bandgap, have a stripe-shaped double hetero pn junction laminated on a semiconductor substrate, and are defined as the stripe. A light confinement region in which the refractive index of the portion to be formed has a relatively higher refractive index than the outside of the stripe, and is configured so that light propagates along the stripe; A high-reflection end face formed by cleaving the semiconductor substrate on a plane perpendicular to the direction, and a traveling direction of light that is located on the opposite side of the high-reflection end face and propagates through the light confinement region. A low-reflection end face formed by cleaving the semiconductor substrate on a plane inclined from a plane perpendicular to the semiconductor substrate; A semiconductor light amplifying means including: a pole; a light guide of the external light reflecting means and a light of the front semiconductor light amplifying means disposed between the external light reflecting means and the low reflection end face of the semiconductor light amplifying means. An optical waveguide that is optically coupled to the confinement region and that is integrally formed with the external light reflecting means, and that at least a part of the optical waveguide can change a refractive index with respect to propagating light. An external cavity semiconductor laser, comprising: a connection optical waveguide means including a rate variable section; 2. The apparatus according to claim 1, wherein said external light reflecting means, said semiconductor light amplifying means, and said connection optical waveguide means are respectively mounted on a common substrate and optically coupled. The external cavity type semiconductor laser according to the above. 3. The connecting optical waveguide means, wherein the optical waveguide is formed using a material whose refractive index to propagating light changes according to temperature, and the refractive index variable section can adjust the temperature of the optical waveguide. The external cavity type semiconductor laser according to claim 1, further comprising a temperature controller configured to: 4. The connecting optical waveguide means, wherein the optical waveguide is:
Surrounding a core having a relatively high refractive index with a clad having a relatively low refractive index, and including an inner core having an electro-optical effect disposed coaxially inside the core, wherein the refractive index variable section 3. The external cavity semiconductor laser according to claim 1, further comprising an electrode for applying an electric field to an inner core of the optical waveguide. 4. 5. The external light reflecting means, wherein the optical waveguide is:
The temperature controller according to any one of claims 1 to 4, further comprising a temperature adjuster that changes a refractive index of the propagating light periodically along a traveling direction of the light and adjusts a temperature of the optical waveguide. 4. The external cavity semiconductor laser according to any one of the above. 6. The external light reflecting means, wherein the optical waveguide is:
An inner core is disposed coaxially inside the core, has an electro-optic effect, and has an inner core whose refractive index for propagating light periodically changes along the traveling direction of light, and an electric field is applied to the inner core. The external cavity semiconductor laser according to claim 1, further comprising an electrode for adding. 7. A Mach-Zehnder core structure connected to an optical waveguide of said external light reflecting means, wherein one path branches into two paths and then merges into one path again. A portion branched into at least two paths, including an inner core having an electro-optical effect disposed coaxially with the core, and including an external light modulation unit having an electrode for applying an electric field to the inner core. The external cavity type semiconductor laser according to claim 1, wherein: 8. The semiconductor optical amplifier according to claim 1, wherein said active layer has a portion where the thickness of said active layer is gradually reduced toward said low reflection end side. 4. The external cavity type semiconductor laser according to item 1. 9. The semiconductor optical amplifier according to claim 1, wherein the semiconductor optical amplifier has a portion where the stripe width of the active layer gradually increases toward the low reflection end face. The external cavity type semiconductor laser according to the above. 10. The semiconductor optical amplifying means has a portion in which at least one of the thickness and the stripe width of the active layer is constant including a portion in contact with the low reflection end face. Or an external cavity semiconductor laser according to item 9. 11. The external cavity semiconductor laser according to claim 1, wherein the semiconductor laser is used as a plurality of light sources constituting an optical circuit device. 12. An inner core having an electro-optical effect and surrounding a core having a relatively high refractive index with a clad having a relatively low refractive index and being coaxially arranged inside the core. An optical waveguide device comprising: an optical waveguide; and an electrode for applying an electric field to an inner core of the optical waveguide. 13. A core having a Mach-Zehnder type core structure in which one path branches into two paths and then merges into one path again, and a portion of the core that branches into at least two paths is provided. An optical waveguide, comprising: an optical waveguide having an inner core having an electro-optic effect disposed coaxially with the core; and an electrode for applying an electric field to the inner core of the optical waveguide. apparatus.