JP4909159B2 - Semiconductor waveguide device, manufacturing method thereof, and semiconductor laser - Google Patents

Description

  The present invention relates to a semiconductor waveguide device used as a light source for optical fiber communication, a light source for optical measurement, a manufacturing method thereof, and a semiconductor laser, and more particularly, a wavelength tunable light source for optical wavelength (frequency) multiplexing systems in optical communication, and a broadband wavelength. It is suitable for a wavelength tunable light source for optical measurement that covers the band.

  While research on optical wavelength (frequency) multiplex communication systems has been conducted in response to an increase in communication information, a wide range of wavelength adjustment functions are required as a light source for transmission and a tunable light source for synchronous detection. In the field of optical measurement, it is desired to realize a wavelength tunable light source that covers a wide wavelength band.

  Various variable wavelength light sources have been studied so far, and they can be broadly divided into those that change continuously in one oscillation mode and those that change discontinuously with mode jumping. Can be divided. In consideration of application to an actual system, it is preferable that the wavelength changes continuously from the viewpoint of controllability. In order to control the wavelength change, two types are mainly used: one that controls the refractive index by changing the temperature and one that uses the refractive index change by current injection. Faster wavelength switching is possible by using the refractive index change by injection.

  Distributed lasers (DBR lasers) and double waveguide lasers (TTG lasers) have been studied as semiconductor lasers that can continuously change the oscillation wavelength using the refractive index change caused by current injection. As the continuous wavelength variable width, a value of 4.4 nm is reported for the DBR laser and 7 nm for the TTG laser. In recent years, so-called short cavity DBR lasers in which the active layer region is shortened in order to suppress the mode jump of the DBR laser have been studied.

  As the discontinuous wavelength variable width with mode jump, a value of 10 nm is obtained in the DBR laser. Further, as a semiconductor laser that is discontinuous but has a wide wavelength tunable width, a Y-branch laser, a super-periodic structure diffraction grating laser, and the like have been prototyped, and a wavelength tunable width of 50 nm to 100 nm has been obtained.

However, the above prior art has the following problems.
In the TTG laser, a current is injected into an active waveguide layer that amplifies light to cause a laser oscillation operation, and a current is independently supplied to a wavelength control inactive waveguide layer formed in the immediate vicinity of the active waveguide layer. By injecting, the oscillation wavelength is changed. Here, if the period of the diffraction grating is Λ and the equivalent refractive index of the waveguide is n, the Bragg wavelength λb is expressed by the following equation (1).
λb = 2nΛ (1)

The laser oscillates in one resonance longitudinal mode near this Bragg wavelength. When current is injected into the inactive waveguide layer, the equivalent refractive index of the waveguide changes, and the Bragg wavelength also changes in proportion to the equation (1). Here, the change rate Δλb / λb of the Bragg wavelength is equal to the change rate Δn / n of the equivalent refractive index as shown in the following equation (2).
Δλb / λb = Δn / n (2)

In addition, the resonance longitudinal mode wavelength also changes as the equivalent refractive index changes due to current injection. In the case of a TTG laser, since the equivalent refractive index of the entire resonator changes uniformly, the change rate Δλr / λr of the resonant longitudinal mode wavelength becomes equal to the change rate Δn / n of the equivalent refractive index.
Δλr / λr = Δn / n (3)

  From the formulas (2) and (3), in the TTG laser, the change in the Bragg wavelength is equal to the change in the resonant longitudinal mode, so that the oscillation wavelength continuously changes while maintaining the first resonant mode. Has characteristics.

  However, in order to perform single transverse mode oscillation operation, the width of the double waveguide needs to be 1 μm to 2 μm, and the thickness of the n-type spacer layer formed between the active layer and the wavelength control layer Since it is necessary to reduce the thickness to 1 μm or less, the buried structure used in a normal semiconductor laser cannot be formed, and a structure for efficiently injecting current into each waveguide layer is manufactured. There was a problem that it was very difficult. Further, since it is different from a normal semiconductor laser structure, it is difficult to integrate with a semiconductor optical amplifier or the like, and there is a problem that a multifunctional integrated device cannot be configured.

In contrast, the DBR laser has a structure in which an active waveguide layer and an inactive waveguide layer for amplifying light are connected in series. Therefore, a buried stripe structure for current confinement as in a normal semiconductor laser is used. Further, independent current injection into each waveguide layer can be easily realized by separating the electrodes formed above each waveguide layer. The mechanism for changing the Bragg wavelength by changing the equivalent refractive index by injecting current into the inactive waveguide layer is the same as that of the TTG laser, but the region where the equivalent refractive index changes is limited to a part of the resonator. For this reason, the change amount of the Bragg wavelength does not match the change amount of the resonance longitudinal mode wavelength. The change ratio Δλr / λr of the resonant longitudinal mode wavelength is shorter than the change ratio Δn / n of the equivalent refractive index by the ratio of the effective length Le of the distributed reflector to the total resonator length L.
Δλr / λr = (Le / L) · (Δn / n) (4)

  Therefore, from the equations (2) and (4), the DBR laser has a drawback that the mode jump occurs because the Bragg wavelength and the resonance longitudinal mode wavelength are relatively separated as the wavelength control current is injected. It was. In order to prevent mode jumping, it is necessary to provide a phase adjustment region in which no diffraction grating is formed, and to match the amount of change in the resonant longitudinal mode and the amount of change in the Bragg wavelength by injecting current there.

  However, this method requires an external circuit for controlling the wavelength control current to the two electrodes, and there is a problem that the device structure and control become complicated. Another method that does not cause mode jump is a short cavity DBR laser that shortens the cavity length and widens the longitudinal mode interval. However, it is necessary to shorten the active layer, and it is difficult to obtain a large output. There was a problem of being.

  The continuous wavelength tunable width in the TTG laser and the DBR laser is limited to the amount of change in the refractive index of the wavelength control layer, and the value remains at about 4 nm to 7 nm. In order to further widen the wavelength variable width, it is necessary to use a means that allows mode jumping and that the wavelength change amount of the wavelength filter is larger than the refractive index change amount. Both the Y-branch laser and the super-periodic structure diffraction grating laser use a means for increasing the filter wavelength change amount more than the refractive index change amount. In these lasers, in order to change the filter wavelength greatly and to obtain sufficient wavelength selectivity, it is necessary to control the current flowing through the two electrodes, and also to provide an electrode for controlling the resonance longitudinal mode wavelength. Become. As a result, in order to adjust the oscillation wavelength, it is necessary to control the injection current to the three electrodes, and there is a problem that the control becomes very complicated.

  In order to solve these problems, the oscillation wavelength can be continuously changed by about 4 nm to 7 nm by controlling the injection current to one electrode, and the current injection to the active waveguide layer and the inactive waveguide layer is also efficient. A semiconductor laser has been developed that can change the oscillation wavelength over a range of about 50 nm to 100 nm by obtaining a semiconductor laser that can be performed well and mode jumping, but with an injection current to two electrodes. Non-Patent Document 1 and Patent Document 1 disclose the structure of a distributed active DFB laser (TDA-DFB-LD). According to this structure, the active layer volume can be sufficiently secured, so that high output can be achieved.

  FIG. 13 shows the structure of a distributed active DFB laser disclosed in Non-Patent Document 1. FIG. 13A is a top view of the distributed active DFB laser, and FIG. 13B is an xx ′ cross-sectional view in FIG.

  As shown in FIG. 13, the distributed active DFB laser has an active waveguide layer 602 and an inactive waveguide layer (wavelength control region) 603 alternately on the lower clad 601 with constant lengths La and Lt, respectively. It has a structure that is periodically coupled in series. An upper clad 604 is formed on the active waveguide layer 602 and the non-active waveguide layer 603, and unevenness, that is, a diffraction grating 605 is formed between the active waveguide layer 602 and the non-active waveguide layer 603 and the upper clad 604. Is formed. Further, an active layer electrode 607 and a wavelength control electrode 608 are provided on the upper clad 604 corresponding to the active waveguide layer 602 and the inactive waveguide layer 603, respectively. A common electrode 610 is provided below the lower clad 601. In this distributed active DFB laser, gain is generated along with light emission by injection of the current Ia into the active waveguide layer 602, and according to the period of the diffraction grating 605 formed between the active waveguide layer 602 and the upper cladding 604. Only the wavelength is selectively reflected to cause laser oscillation.

On the other hand, when the current It is injected into the inactive waveguide layer 603, the refractive index of the inactive waveguide layer 603 changes due to the plasma effect generated according to the carrier density, and accordingly, the inactive waveguide layer 603 is changed. The optical period of the diffraction grating 605 formed between the upper cladding 604 and the upper cladding 604 changes. Then, the equivalent refractive index of the inactive waveguide layer 603 changes, and the resonant longitudinal mode wavelength is shifted to the short wavelength side by the ratio of the length of the wavelength control region to the length of one cycle. If the length of one cycle of the repetitive structure is L and the wavelength control region length is Lt, the rate of change of the resonance longitudinal mode wavelength is expressed by the following equation (5).
Δλr / λr = (Lt / L) · (Δn / n) (5)

On the other hand, each wavelength of the plurality of reflection peaks is also shifted to the short wavelength side as a result of a change in equivalent refractive index due to current injection. Since the reflection peak wavelength is proportional to the average equivalent refractive index change within one period of the repetitive structure, the change ratio Δλs / λs of the reflection peak wavelength is expressed by the following equation (6).
Δλs / λs = (Lt / L) · (Δn / n) (6)

  From the equations (5) and (6), the reflection peak wavelength and the resonance longitudinal mode wavelength are shifted by the same amount. Therefore, in this laser, the wavelength continuously changes while maintaining the mode in which it oscillates first.

The structure of the distributed active DFB laser disclosed in Patent Document 1 is shown in FIG.
Similarly to the distributed active DFB laser shown in FIG. 13, this distributed active DFB laser has an active waveguide layer 702 and an inactive waveguide layer 703 alternately formed on the lower clad 701 with constant lengths La and Lt, respectively. An upper clad 704 is formed on the active waveguide layer 702 and the non-active waveguide layer 703, and has an irregularity between the active waveguide layer 702 and the upper clad 704. A diffraction grating 705 is formed. Furthermore, an active layer electrode 707 and a wavelength control electrode 708 are provided on the upper clad 704 corresponding to the active waveguide layer 702 and the inactive waveguide layer 703, respectively. A common electrode 710 is formed below the lower clad 701. In this distributed active DFB laser, the diffraction grating 705 is formed only partially, but the wavelength continuously changes in the same manner as the distributed active DFB laser of FIG.

  Further, in Patent Document 1, as shown in FIG. 15, it has the same structure as the distributed active DFB laser shown in FIG. 14, and the repetition period of the active waveguide layer 702 and the inactive waveguide layer 703 is L1, A structure in which two different lasers L2 are coupled in series is also disclosed. Note that members that are substantially the same as those shown in FIG. 14 are given the same reference numerals, and descriptions thereof are omitted.

Japanese Patent No. 3237733 Ishii et al., “A Tunable Distributed Amplification DFB Laser (TDA-DFB-LD)”, IEEE Photonics Letters, vol.10, no.1, January 1998, p.30-32

  However, in the above-described structure of the distributed active DFB laser, the active region and the inactive region are alternately repeated with a short region length, so that the leakage current flowing from the active region electrode to the inactive flow region or vice versa The leakage current flowing from the region electrode to the active region cannot be ignored. There are problems that wavelength control cannot be performed accurately and the wavelength control range becomes narrow due to the leakage current flowing between them.

  In general, as a method of increasing the electrode separation resistance, there is a method of widening the electrode interval We between the active region and the non-active region as shown in FIG. 16, but each distributed active DFB laser has a short length of each region. In order to use the region effectively, it is desirable that the electrode intervals be as close as possible. On the other hand, there are a method of providing a separation groove 914 between the electrodes as shown in FIG. 17A and a method of increasing resistance by implanting impurity ions as shown in FIG. If the depth d of the separation groove 914 is deeper, the electrode separation resistance can be increased. However, if the separation groove 914 is too deep, reflected waves increase due to the difference in refractive index between the semiconductor and the separation groove 914 when the light propagates through the waveguide. Become. Even in the method by implanting impurity ions, the problem of reflection occurs as in the case of the separation groove 914 due to the influence of the change in refractive index. For this reason, a problem different from the leakage current occurs, such as an unexpected resonance mode.

  Accordingly, an object of the present invention has been proposed in view of the above-described problems, and a semiconductor waveguide element that suppresses the influence of a reflected wave due to ion implantation or separation grooves while increasing the electrode separation resistance while keeping the electrode interval narrow. A manufacturing method thereof and a semiconductor laser are provided.

A semiconductor waveguide device according to a first invention that solves the above-described problems includes a first semiconductor cladding layer, an optical waveguide layer having a higher refractive index than that of the first semiconductor cladding layer, and a refractive index higher than that of the optical waveguide layer. Are two or more optical waveguides each including at least one second semiconductor cladding layer, which are coupled in series in the waveguide direction, and each of the optical waveguides is independently supplied with current. A separation electrode having a conductivity type different from that of the second semiconductor cladding layer or an insulating separation layer provided between adjacent electrodes in the second semiconductor cladding layer; normal of plane intersecting the waveguide direction, the waveguide direction in pairs and inclined by the inclination angle theta, or the inclination angle of the adjacent separating layer theta are different from each other, when the inclination angle of the adjacent separating layer theta is equal to Is between adjacent separation layers x is to satisfy the x> 2d / sin (2θ) .

  A semiconductor waveguide device according to a second invention for solving the above-mentioned problem is the semiconductor waveguide device according to the first invention, wherein the separation layer ion-implants impurities into the second semiconductor cladding layer or It is formed by diffusing.

  A semiconductor waveguide device according to a third invention for solving the above-described problem is the semiconductor waveguide device according to the first invention or the second invention, and between adjacent electrodes in the second semiconductor cladding layer. A separation groove is provided.

  A semiconductor waveguide device according to a fourth invention that solves the above-described problem is a semiconductor waveguide device according to any one of the first to third inventions, and is arranged in the waveguide direction of the separation layer. The normal line of the intersecting surface is inclined by 5 degrees or more with respect to the waveguide direction.

  A semiconductor waveguide device according to a fifth invention for solving the above-described problem is a semiconductor waveguide device according to any one of the first invention to the third invention, and is arranged in the waveguide direction of the separation layer. The normal of the intersecting surface is inclined at an angle of 20 degrees to 55 degrees with respect to the waveguide direction.

  A semiconductor waveguide device according to a sixth invention for solving the above-described problem is a semiconductor waveguide device according to any one of the first to fifth inventions, and is arranged in the waveguide direction of the separation layer. All of the intersecting surfaces are characterized by having an equal inclination angle with respect to the waveguide direction.

  A semiconductor waveguide device according to a seventh invention that solves the above-described problem is a semiconductor waveguide device according to any one of the first to fifth inventions, and is arranged in the waveguide direction of the separation layer. It is characterized in that every other crossing plane has an equal inclination angle, and the separation layers adjacent along the waveguide direction are mutually symmetric with respect to a plane perpendicular to the waveguide direction.

A semiconductor waveguide device according to an eighth invention for solving the above-described problems is a semiconductor waveguide device according to any one of the first invention to the seventh invention, wherein the second semiconductor clad layer includes: The end of the hole formed in the insulating film provided on the upper surface intersects the waveguide direction of the hole, or the end of the electrode intersects the waveguide direction, or both of them correspond to the corresponding separation layer. It is characterized by being formed in parallel to.

A semiconductor waveguide device according to a ninth invention for solving the above-described problem is a semiconductor waveguide device according to any one of the first to eighth inventions, wherein a coupling surface of the optical waveguide layer is provided. And having a slope equal to that of the separation layer.

A semiconductor waveguide device according to a tenth invention for solving the above-described problem is a semiconductor waveguide device according to any one of the first to ninth inventions, and is a semi-insulating material doped with ruthenium. A current blocking layer is provided.

A semiconductor laser according to an eleventh invention for solving the above-described problems is characterized by using the semiconductor waveguide device according to any one of the first invention to the tenth invention.

A method of manufacturing a semiconductor waveguide device according to a twelfth aspect of the present invention that solves the above-described problem includes a first semiconductor cladding layer, an optical waveguide layer having an optical refractive index larger than that of the first semiconductor cladding layer, and the optical waveguide. Two or more optical waveguides each including one or more second semiconductor clad layers having a refractive index smaller than that of the waveguide layer are coupled in series in the direction of the optical waveguide, and electrodes for supplying current independently to the optical waveguide are provided. A method of manufacturing a semiconductor waveguide device provided, wherein an impurity is ion-implanted or diffused between adjacent electrodes in the second semiconductor cladding layer to have a conductivity type different from that of the second semiconductor cladding layer, or insulative, extends in a direction crossing the waveguide direction, a step of forming a separation layer having a slope with respect to a direction perpendicular to the waveguide direction, the waveguide of the separating layer The normals of the planes that intersect the direction are inclined with respect to the waveguide direction by the inclination angle θ, and the adjacent separation layers are adjacent when the inclination angles θ are different from each other or the inclination angles θ of the adjacent separation layers are equal. The separation layer interval x satisfies x> 2d / sin (2θ) .

  According to the semiconductor laser of the present invention, the active region and the non-active region can be alternately arranged because the electrode separation resistance can be increased while suppressing the influence of the ion implantation and the reflected wave due to the separation groove while keeping the electrode interval narrow. Even in a structure such as a distributed active DFB laser having a repeated structure, the leakage current flowing between the mutual regions can be reduced, the wavelength control range can be expanded, and the wavelength control can be accurately performed.

  The best mode of the present invention will be described in detail in the following examples.

  A first embodiment of the present invention will be described in detail with reference to FIGS.

  FIG. 1A is a top view of a semiconductor laser according to the present embodiment, FIG. 1B is a cross-sectional view taken along line xx ′ shown in FIG. 1A, and FIG. FIG. 1D is a top view of the semiconductor laser according to the present embodiment with the electrodes and the insulating film removed, and FIG. 1E is a top view of the semiconductor laser according to the present embodiment. 2 is a cross-sectional view taken along line yy ′ of FIG. 1, FIG. 2 is a top view illustrating another example of the semiconductor laser according to the present embodiment, and FIG. 3 illustrates light refraction at a boundary surface between substances having different refractive indexes. FIG. 4 is a graph showing the relationship between the band gap wavelength and the refractive index difference, and FIG. 5 is a graph showing the coupling rate of the reflected wave with respect to the incident angle to the refractive index boundary.

  As shown in FIG. 1, the semiconductor laser according to this example has an optical refractive index higher than that of the lower cladding 1 on the lower cladding (semiconductor substrate) 1 that is the first semiconductor cladding layer made of n-type InP. Each includes one or more waveguide layers 15 and an upper cladding 4 that is a second semiconductor cladding layer having a refractive index smaller than that of the optical waveguide layer 15.

  The optical waveguide layer 15 is configured by periodically coupling the active waveguide layer 2 and the inactive waveguide layer 3 in series along the light propagation direction. The active waveguide layer 2 has an optical gain with respect to light in the oscillation wavelength band, and is an active region having a length La made of GaInAsP. The inactive waveguide layer 3 has no optical gain, and is a non-active region having a length Lt made of GaInAsP having a composition different from that of the active waveguide layer 2 and is a wavelength control region. In the present example, the region lengths La and Lt were each 29.5 μm, and the repetition period L (= La + Lt) of the active waveguide layer 2 and the inactive waveguide layer 3 was 59 μm.

  An upper clad 4 made of p-type InP is formed on the active waveguide layer 2 and the inactive waveguide layer 3, and a light propagation direction (hereinafter referred to as a light guide) is formed between the optical waveguide layer 15 and the upper clad 4. A diffraction grating 5 is formed in which concaves and convexes are formed at the same period over the entire length and the equivalent refractive index of the optical waveguide layer 15 is periodically modulated. In this example, the diffraction grating period was set to 243 nm in order to obtain an oscillation wavelength of 1.55 μm.

  On the upper cladding 4, a contact layer 6 having a multilayer structure of highly doped p-type InGaAsP and / or InGaAs is provided for ohmic contact between the active waveguide layer 2 and the inactive waveguide layer 3, and An active layer electrode 7 and a wavelength control electrode 8 are provided thereon so as to correspond to the active waveguide layer 2 and the inactive waveguide layer 3, respectively.

  Between the active region and the non-active region, ion implantation of Si (silicon) is performed so as to become an n-type semiconductor (ion implantation region (conductivity type separation layer) 16).

  The position where the conductivity type of the semiconductor is inverted by ion implantation (conduction type inversion region) can be efficiently prevented from leaking current between the mutual regions by providing the center of the boundary between the active region and the inactive region. It is not always necessary to provide the center of the boundary between the active region and the non-active region, and the effect of ion implantation can be obtained even if it is disposed at a position offset from either region. In the case of the distributed active DFB laser of this embodiment, a relatively large current is injected in the active region in order to generate a sufficient gain for obtaining a desired oscillation output, and in the wavelength control region (inactive region). Control the current from a relatively small current to control the wavelength.

  Therefore, in many cases, a leakage current flows from the active region to the inactive region because the bias voltage of the inactive region is lower than that of the active region. In this case, it is possible to enhance the effect of suppressing leakage current by shifting the center of ion implantation to the active region side instead of arranging it at the connection portion between the active region and the inactive region.

  All the active layer electrodes 7 and the wavelength control electrodes 8 are integrated with each other and are short-circuited on each other. A common electrode 10 is formed at the bottom of the substrate, that is, below the lower cladding 1.

  When GaInAsP having a band gap wavelength of 1.55 μm is used for the active waveguide layer 2, a laser having a band gap wavelength shorter than that, for example, GaInAsP having a band gap wavelength of 1.4 μm, is used for the inactive waveguide layer 3. Since it does not contribute to the oscillation gain, the carrier density is not constant. Thereby, the refractive index can be changed greatly by current injection.

  The active waveguide layer 2 and the inactive waveguide layer 3 do not have to be a bulk material. For example, a quantum well structure, a multilayer quantum well structure in which a quantum well is sandwiched between barrier layers, a quantum wire, a quantum dot, or the like Further, it may have a low-dimensional quantum well structure. In order to enhance light confinement and carrier confinement in the active layer, a separate confinement heterostructure (SCH) that introduces a layer having a refractive index between the active layer and the clad layer may be introduced.

  The semiconductor using this element is not limited to the combination of InP and GaInAsP, and may be another semiconductor such as GaAs, GaInNAs, AlGaInAs, InAs, and GaInNAs. The active waveguide layer 2 and the inactive waveguide layer 3 The combination of the band gap wavelengths is not limited to the above.

  As shown in FIG. 1A, the active electrodes 7 and the wavelength control electrodes 8 are integrated with each other to form a comb shape. As shown in FIG. 1B, an insulating film 9 is formed under the active layer electrode 7 and the wavelength control electrode 8. A hole 9a as an electrode window as shown in FIG. 1C is formed in the insulating film 9 immediately above the waveguide and corresponding to the active region and the non-active region, and the contact layer 6 is exposed. It is supposed to be. In other words, the optical waveguide layer 15 formed along the waveguide direction is located below the hole 9a. Also, below the insulating film 9, contact is made along the waveguide direction as shown in FIGS. 1D and 1E so that the contact layer 6 is left only on the waveguide in each region. Etched at a depth d to leave layer 6.

  And as shown in FIG.1 (d), the contact layer 6 is formed in the parallelogram-like island shape. Thereby, separation grooves 14 for separating the contact layer 6 having an angle with respect to the waveguide direction are formed between the regions. By performing ion implantation on portions other than the contact layer 6, the conductivity type changes at the location where the ions are implanted. For example, between the contact layer 6 and the adjacent contact layer 6, p-type, n-type, p-type As a result, no current flows. In addition, the ion implantation region also has an angle with respect to the waveguide. In this embodiment, all the regions other than the island-shaped contact layer 6 are ion-implanted, but at least the conductivity type around the contact layer 6 may be reversed. The width Wa of the contact layer 6 was 5 μm, and the distance between adjacent contact layers 6 along the waveguide was 5 μm. Ion implantation was performed 1 μm away from the island-shaped contact layer 6.

  Further, as shown in FIG. 1E, p-type semiconductors 11 and n-type semiconductors 12 made of InP are alternately formed as current blocking layers 13 on both sides of the optical waveguide layer 15 having a width Ws, and buried heterostructures ( BH). Thereby, a current is efficiently injected into the active waveguide layer 2 or the inactive waveguide layer 3. In the present embodiment, the current blocking layer 13 is realized by combining p-type InP and n-type InP, but semi-insulating InP doped with Fe (iron), Ru (ruthenium) or the like may be used. In this embodiment, the waveguide width Ws is 1.5 μm.

  As shown in FIG. 1C, after the contact layer 6 and the upper cladding 4 are covered with the insulating film 9, a hole 9a is formed only in the portion of the insulating film 9 corresponding to the current Ia or It injection portion (FIG. 1). Then 8 places). The shape of the hole 9a is usually a rectangle. Even if it is a rectangle, the effect of the present invention can be obtained, but the manufacturing process is facilitated by using the same parallelogram as the shape of the contact layer 6. That is, as shown in FIG. 1 (e), a step is formed on the surface of the substrate in which the contact layer 6 is convex, and a pattern for punching the insulating film 9 with a photoresist is formed here. It becomes. The resist thickness of the step portion is not necessarily uniform, and the thickness is often smoothly changed according to the distance from the step. By matching the shape of the contact layer 6 with the shape of the hole, the hole pattern has a constant distance from the step, and thus the pattern can be made uniformly.

  As shown in FIG. 1A, the electrode patterns of the active layer electrode 7 and the wavelength control electrode 8 also reflect the shapes of the contact layer 6 and the insulating film 9, and the plane intersecting the waveguide direction is in the waveguide direction. Wiring is performed so as to incline with respect to the orthogonal direction. Similarly to the hole 9a, the active layer electrode 7 and the wavelength control electrode 8 may be drawn out in a direction orthogonal to the waveguide direction, but the electrode pattern is also formed by lift-on using a photoresist or wet etching. It is desirable to perform wiring so that the influence of the step is reduced as much as possible. Therefore, the shape shown in FIG. 2 may be used instead of the shape shown in FIG.

  When the shape of the contact layer 6 is a parallelogram in top view as in this embodiment, the element area is affected depending on which side the active layer electrode 7 and the wavelength control electrode 8 are drawn out. For example, in this embodiment, when the wavelength control electrode 8 is integrated on the y side in FIG. 1A and the active layer electrode 7 is integrated on the y ′ side in FIG. Since it is necessary to further increase the substrate area in the waveguide direction, that is, before and after the light propagation direction, it is necessary to couple extra waveguides. Therefore, as shown in FIG. 1A, the electrode lead-out direction can be reduced while the electrode located at the end with respect to the waveguide direction is drawn out while being inclined toward the center of the element, thereby reducing the substrate area. .

  Next, an example of a manufacturing method of the distributed active DFB laser according to the present embodiment will be described.

First, an active waveguide layer 2 is formed on the lower cladding 1 made of n-type InP by metal organic vapor phase epitaxy. Next, a part of the active waveguide layer 2 is etched using SiO ₂ or SiN as a mask. Using the etching mask as it is, the inactive waveguide layer 3 is produced by a selective growth method. Thereafter, a diffraction grating pattern is formed on the applied resist by using an electron beam exposure method, and the semiconductor is etched using this as a mask to form the diffraction grating 5.

After re-growing a part of the upper clad 4 made of p-type InP by metal organic vapor phase epitaxy, a waveguide is formed in a stripe shape having a width of 1.5 μm using SiO ₂ or SiN as a mask in order to suppress the transverse mode. Process. Using the etching mask as it is, an InP current blocking layer 13 made of the p-type semiconductor 11 / n-type semiconductor 12 is grown on both sides of the striped waveguide by a selective growth method.

Thereafter, the selective growth mask is removed, and the remaining InP upper cladding layer 4 and GaInAs contact layer 6 are grown. Next, the contact layer 6 is etched into a parallelogram island shape using a SiN mask, and Si ions are implanted into portions other than the contact layer 6 using the SiN mask. Ion implantation was performed in two stages. The first ion implantation is performed under the condition of an acceleration voltage of 70 keV and a dose amount of 5 × 10 ¹³ cm ⁻² , and the second ion implantation is performed under the condition of an acceleration voltage of 200 keV and a dose amount of 1.0 × 10 ¹⁴ cm ⁻² . went. After the implanted ions are activated by heat treatment at 700 ° C. for 1 minute, a SiO ₂ insulating film 9 is formed, and currents Ia or It of the insulating film 9 on the active waveguide layer 2 and the inactive waveguide layer 3 are formed. A hole 9a is opened in a portion corresponding to the injection portion. An electrode pattern is formed by lift-off so that the active layer electrodes 7 and the non-active layer electrodes 8 are short-circuited on the element.

  The semiconductor growth method is not limited to the metal organic vapor phase epitaxial growth method, and a molecular beam epitaxial growth method or other means may be used. The method of forming the diffraction grating is not limited to the electron beam exposure method, and a two-bundle interference exposure method or other means may be used.

  Further, as a method of etching a part of the contact layer 6 and the upper clad 4, the active waveguide layer 2 and the inactive waveguide layer 3 are short in length and have a short repetition period. Although an etching method with a small amount of side etching such as etching is desirable, there is no problem even with a wet etching method.

  The ion species used when the p-type is inverted to the n-type by ion implantation may be other ions such as C (carbon) and S (sulfur) instead of Si (silicon). In this embodiment, since an n-type semiconductor substrate is used, p-type InP is used for the clad and it is necessary to invert the p-type to the n-type. In the case of the n-type InP clad, Conversely, it is necessary to invert the n-type to the p-type, and Be (beryllium), Mg (magnesium), or the like may be implanted. Alternatively, Fe (iron), Ru (ruthenium), or the like may be ion-implanted to form a semi-insulator.

  In the present embodiment, the structure in which the active waveguide layers 2 and the inactive waveguide layers 3 are alternately and periodically described has been described as an example. Therefore, the active waveguide layer is not limited to the combination of the active waveguide layer 2 and the inactive waveguide layer 3, and the active waveguide layer is divided into a plurality of regions, or the inactive waveguide is divided into a plurality of inactive waveguide layers. The present invention can be applied even when the electrodes are provided by being divided into regions.

  As described above, when there are a plurality of regions, the influence of the leakage current appears remarkably, but even when there are only two regions, the present invention suppresses the leakage current flowing between them and guides them. This is useful for suppressing reflection of light.

  In this embodiment, since an example of application to a distributed active DFB laser has been shown, the structure in which the electrode on the active waveguide layer 2 and the electrode on the inactive waveguide layer 3 are short-circuited on the element has been described. However, the present invention can be applied even if each electrode is independent. Further, even if it is not a distributed active DFB laser, for example, it can be applied to an electrode of a laser part and an electrode part of a modulator in a device in which a laser and a modulator are integrated. That is, it can be applied to separation between different waveguide elements connected in series.

  Subsequently, the operation of the present embodiment will be described.

When an impurity is implanted by ion implantation, the refractive index changes because the region is made of a material different from the conventional material. Reflection of light occurs at the interface between materials having different refractive indexes. For example, as shown in FIG. 3, if light enters the junction interface 19 between the material 20 having a refractive index N ₁ and the material 21 having a refractive index N ₂ from the material 20 side, the light is reflected at the junction interface. The rate R is expressed by the following equation (7).
R = ((N ₁ −N ₂ ) / (N ₁ + N ₂ )) ² (7)

  That is, the light reflectance R is determined by the difference in refractive index between the substances 20 and 21. For this reason, the light propagating through the waveguide is reflected when it is applied to a region where the refractive index has been changed by ion implantation. As the depth of ion implantation increases, the ratio related to the optical field increases and the difference in equivalent refractive index increases. Note that when the ion implantation region has a shape perpendicular to the waveguide, reflected light is generated due to reflection, and thus the device characteristics are affected by mode instability.

  In the distributed active DFB laser according to the present embodiment, since the refractive index change caused by ion implantation is not so large, the refractive index difference is small and the absolute value of the reflectance is very small. However, on the other hand, as shown in FIG. 1, a plurality of isolation regions exist in one element (distributed active DFB laser in this embodiment). For this reason, there is a possibility that the reflection of light cannot be ignored in one entire element. Therefore, in an element having a plurality of separation regions, it is important to keep the reflectance R as low as possible, or to prevent a reflected wave from being coupled to the waveguide even if reflection occurs.

When light is incident obliquely on the boundary surfaces of materials having different refractive indexes, when the incident angle is θ ₁ and the refraction angle is θ ₂ , the following equation (8) is expressed according to Snell's law. Thus, refraction occurs at the boundary surface.
sin θ ₁ / sin θ ₂ = N ₂ / N ₁ (8)

Here, when the incident angle θ ₁ coincides with the Brewster angle θ _B , reflection of a component parallel to the incident surface can be eliminated. The Brewster angle θ _B can be expressed by the following equation (9).
θ _B = tan ⁻¹ (N ₂ / N ₁ ) (9)

FIG. 4 shows the relationship between the incident angle θ _{1 of} light incident on the boundary surface 19 shown in FIG. In the present embodiment, the incident angle θ ₁ is an inclination angle of the light propagation direction with respect to the normal line of the boundary surface 19. In the graph shown in FIG. 4, the refractive index of the incident-side material 20 is N ₁ = 3.20, and the refractive index difference Δn between the material 20 and the material 21 having the refractive index N ₂ is Δn = N ₁ −N ₂ = 0. Examples in the case of .005, 0.01, 0.015, and 0.02 are shown.

In this embodiment, since the difference in refractive index between the waveguide portion and the ion implantation region 16 is small, the Brewster angle θ _B is approximately 45 degrees from the equation (9). That is, when the inclination angle θ of the surface intersecting the waveguide direction of the ion implantation region 16 is approximately 45 degrees, the reflectance R becomes 0, and the reflectance R becomes very small near the inclination angle θ = 45 degrees. .

Taking the case where the refractive index difference Δn = 0.01 as an example, the reflectance R can be reduced when the incident angle θ ₁ is 20 degrees or more and 55 degrees or less from FIG. In particular, in order to suppress the reflectance R to less than half when light is incident perpendicular to the boundary surface, that is, when the incident angle θ ₁ = 0, the incident angle θ _{1 is set} to about 28 to 52 degrees. A value between may be used. Further, in order to suppress the reflectance R to one third or less of the reflectance R at the incident angle θ ₁ = 0, the incident angle θ ₁ may be set to a value between about 33 degrees and 51 degrees. As can be seen from Fig. 4, more incident angle theta ₁ is a Brewster angle theta _B lower than about, the incident angle theta ₁ is compared with greater than Brewster angle theta _B, reflection with respect to the incident angle theta ₁ The change in the rate R is moderate.

Note that it is not always necessary to suppress all reflections at the boundary surface, and if the reflected wave does not have to be coupled to the waveguide even if reflection occurs, the selection range of the incident angle θ ₁ can be expanded as follows. .

FIG. 5 shows the relationship between the incident angle to the boundary surface and the coupling ratio of the reflected wave to the waveguide when the optical mode field width is 1.5 μm. Note that the reflected wave coupling rate is a reflection when the incident angle θ ₁ = 0, that is, when the boundary surface is orthogonal to the waveguide direction so that the difference in refractive index at the boundary surface may not be taken into consideration. The coupling rate of the wave to the waveguide is shown as 1.

From FIG. 5, if the incident angle θ ₁ is about 5 ° or more, the reflected wave coupling rate to the waveguide can be reduced to half. In order to reduce the reflected wave coupling rate to about 30% or less, the incident angle θ ₁ is about 7%. It is understood that the incident angle θ ₁ should be approximately 9 degrees or more in order to reduce the reflected wave coupling ratio by one digit.

  Therefore, in the case of the present embodiment, if the ion implantation region 16 is formed so that the refractive index boundary surface has the above angle with respect to the direction orthogonal to the waveguide direction, the reflectance caused by the refractive index difference due to the impurity can be reduced. And the coupling of the reflected wave to the waveguide can be reduced. Therefore, the reflectivity can be suppressed even if the ion implantation depth is increased to increase the separation resistance and the difference in equivalent refractive index is increased.

  In this embodiment, ion implantation is used to change the conductivity type of the semiconductor. However, although there is a problem that the region is expanded, it can also be realized by a method using thermal diffusion of impurities. Even in such a case, the same effect as in the present embodiment can be obtained by diffusing from the waveguide into the region using the angle.

  In addition, this embodiment can obtain an effect independently regardless of the shape of the butt joint when the active waveguide layer 2 and the inactive waveguide layer 3 are connected. The butt joint can prevent reflection depending on the shape, but crystal regrowth is necessary, and there is an optimal connection surface angle depending on the growth conditions, so the optimal angle for reflection countermeasures is not always good. However, the angle of ion implantation may be determined independently in consideration of region separation and reflection countermeasures.

  However, in terms of fabrication, the crystal growth surface is not flat on the connection surface of the butt joint, and the crystal is not necessarily of high quality, so if ion implantation is performed so as to intersect the connection surface, the ion implantation becomes uneven. Or a path through which current flows only on the butt joint surface may occur. Therefore, by forming the ion implantation region along the connection surface of the butt joint, the separation region can be reliably formed.

  A second embodiment of the present invention will be described in detail with reference to FIG.

  6A is a top view of the semiconductor laser according to the present embodiment, FIG. 6B is an xx ′ cross-sectional view shown in FIG. 6A, and FIG. 6C is the present embodiment. FIG. 6D is a top view of the semiconductor laser according to the present embodiment with the electrodes and the insulating film removed, and FIG. 6E is a top view of the semiconductor laser according to the present embodiment. It is yy 'sectional drawing of Fig.6 (a).

  As shown in FIG. 6, the semiconductor laser according to this example has an optical waveguide having a higher optical refractive index than the lower cladding 101 on the lower cladding (semiconductor substrate) 101 that is the first cladding layer made of n-type InP. Each of the layers 115 includes at least one upper clad 104 that is a second clad layer having a refractive index lower than that of the optical waveguide layer 115.

  The optical waveguide layer 115 is configured by alternately and periodically coupling the active waveguide layer 102 and the inactive waveguide layer 103 in series along the light propagation direction. The active waveguide layer 102 has an optical gain with respect to light in the oscillation wavelength band, and is an active region having a length La made of GaInAsP. The inactive waveguide layer 103 is an inactive region having a length Lt made of GaInAsP having no optical gain and having a composition different from that of the active waveguide layer 102, and is a wavelength control region. In this example, the region lengths La and Lt were 48.7 μm and 24.3 μm, respectively, and the repetition period L (= La + Lt) of the active waveguide layer 102 and the inactive waveguide layer 103 was 73 μm.

  An upper clad 104 made of p-type InP is formed on the active waveguide layer 102 and the inactive waveguide layer 103, and a light propagation direction (hereinafter referred to as a light guide) is formed between the optical waveguide layer 115 and the upper clad 104. A diffraction grating 105 is formed in which irregularities are formed at the same period over the entire length and the equivalent refractive index of the optical waveguide layer 115 is periodically modulated. In this example, the diffraction grating period was set to 242 nm in order to obtain an oscillation wavelength of 1.55 μm.

  A contact layer 106 made of a highly doped p-type InGaAsP and / or InGaAs or a multilayer structure thereof is provided on the upper cladding 104 for ohmic contact between the active waveguide layer 102 and the inactive waveguide layer 103, and An active layer electrode 107 and a wavelength control electrode 108 are provided thereon so as to correspond to the active waveguide layer 102 and the inactive waveguide layer 103, respectively. A common electrode 110 is provided below the lower clad 101. Between the active region and the non-active region, ion implantation is performed on the contact layer 106 and part of the upper cladding 104.

  When GaInAsP having a band gap wavelength of 1.55 μm is used for the active waveguide layer 102, a laser having a band gap wavelength shorter than that, for example, GaInAsP having a band gap wavelength of 1.4 μm, is used for the inactive waveguide layer 103. Since it does not contribute to the oscillation gain, the carrier density is not constant. Thereby, the refractive index can be changed greatly by current injection.

  The active waveguide layer 102 and the inactive waveguide layer 103 do not have to be a bulk material. For example, a quantum well structure, a multilayer quantum well structure in which a quantum well is sandwiched between barrier layers, a quantum wire, a quantum dot, or the like Further, it may have a low-dimensional quantum well structure. In order to enhance light confinement and carrier confinement in the active layer, a separate confinement heterostructure (SCH) that introduces a layer having an intermediate refractive index between the active layer and the cladding layer may be introduced.

  The semiconductor used for this element is not limited to the combination of InP and GaInAsP, and may be another semiconductor such as GaAs, GaInNAs, AlGaInAs, InAs, and GaInNAs, and the band of the active waveguide layer and the inactive waveguide layer. The combination of gap wavelengths is not limited to the above.

  As shown in FIG. 6A, the active layer electrodes 107 and the wavelength control electrodes 108 are arranged independently of each other. For example, if the active layer electrodes 107 and the wavelength control electrodes 108 are short-circuited by wires or the like outside the device, the same operation as in the first embodiment can be obtained. As shown in FIG. 6B, an insulating film 109 is formed under the active layer electrode 107 and the wavelength control electrode 108. In the insulating film 109, holes 109a as electrode windows as shown in FIG. 6 (c) are formed immediately above the waveguide and corresponding to the active region and the non-active region (in FIG. 6, there are 8 holes 109a). ), The contact layer 106 is exposed. In other words, the optical waveguide layer 115 formed along the waveguide direction is positioned below the hole 109a. Below the insulating film 109, the contact layer 106 is provided only on the waveguide in each region, and is sandwiched between the semi-insulators 122. And each area | region is electrically isolate | separated in the area | region which reversed the conductivity type of the semiconductor by ion implantation.

  All the active layer electrodes 107 and the wavelength control electrodes 108 are disposed independently. By configuring the active layer electrodes 107 and the wavelength control electrodes 108 to be short-circuited outside the element by, for example, a wire or the like, the same operation as in the first embodiment of the present invention described above can be obtained. A common electrode 110 is formed at the bottom of the substrate, that is, below the lower clad 101.

  As shown in FIG. 6D, an ion implantation region 116 having an angle with respect to the waveguide is formed between the regions so as to separate the contact layer 106 on the waveguide. Thereby, since the conductivity type of the semiconductor changes only in the ion-implanted region 116, for example, the region from one electrode to the adjacent electrode becomes p-type, n-type, and p-type, and current does not easily flow. The ion-implanted region 116 may be ion-implanted while leaving the contact layer 106, but the effect is noticeable by performing ion implantation after removing the contact layer 106 having a high doping concentration.

  Further, as shown in FIG. 6E, the semi-insulator 122 is formed as a current blocking layer on both sides of the optical waveguide layer 115 having a width Ws to form a buried heterostructure (BH). Thereby, current is efficiently injected into the active waveguide layer 102 or the inactive waveguide layer 103. In this embodiment, the waveguide width Ws is 1.8 μm.

  In the ion implantation region 116, the length Wa in the direction perpendicular to the waveguide needs to be set to be longer than at least the waveguide width Ws = 1.8 μm. Although there is no major problem caused by the fact that the length Wa of the ion implantation region 116 is longer than the width Ws of the waveguide, in this embodiment, contact resistance and electrode routing for injecting the current Ia or It into the waveguide layer 115. The width Wa of the ion implantation region 116 was set to 10 μm in consideration of a size that does not sometimes cause a problem.

  As shown in FIG. 6C, after the contact layer 106, the semi-insulator 113, and the ion implantation region 116 are covered with the insulating film 109, the hole 109a is formed only in the portion of the insulating film 109 corresponding to the current Ia or It implanted portion. (Eight places in FIG. 6). The shape of the hole 109a is usually a rectangle. Even if the shape is rectangular, the effect of the present invention can be obtained, but the manufacturing process can be facilitated by using the same parallelogram as the shape of the contact layer 106. That is, as shown in FIG. 6E, a step is formed on the surface of the substrate in which the contact layer 106 is convex, and a pattern for forming a hole in the insulating film 109 with a photoresist is formed here. It becomes. The resist thickness of the step portion is not necessarily uniform, and the thickness is often smoothly changed according to the distance from the step. By matching the shape of the contact layer 106 with the shape of the hole, the hole pattern has a constant distance from the step, so that the pattern can be formed uniformly.

  As shown in FIG. 6A, the electrode patterns of the active layer electrode 107 and the wavelength control electrode 108 also reflect the shapes of the contact layer 106 and the insulating film 109, and the plane intersecting the waveguide direction is in the waveguide direction. Wiring is performed so as to incline with respect to the orthogonal direction. Similarly to the hole 109a, the active layer electrode 107 and the wavelength control electrode 108 may be drawn out in a direction perpendicular to the waveguide direction, but the electrode pattern is also formed by lift-on using a photoresist or wet etching. It is desirable to perform wiring so that the influence of the step is reduced as much as possible.

  Next, an example of a manufacturing method of the distributed active DFB laser according to the present embodiment will be described.

First, an active waveguide layer 102 is formed on the lower clad 101 made of n-type InP by metal organic vapor phase epitaxy. Next, a part of the active waveguide layer 102 is etched using SiO ₂ or SiN as a mask. The inactive waveguide layer 103 is produced by a selective growth method using the etching mask as it is. Thereafter, a diffraction grating pattern is formed on the applied resist by using an electron beam exposure method, and the semiconductor is etched using this as a mask to form the diffraction grating 105.

After re-growing the upper clad 104 made of p-type InP and the contact layer 106 made of GaInAs by metal organic vapor phase epitaxy, a stripe shape having a width of 1.8 μm using SiO ₂ or SiN as a mask in order to suppress the transverse mode. The waveguide is processed. Using the etching mask as it is, a semi-insulator (semi-insulator current blocking layer) 122 made of a semiconductor doped with Ru (ruthenium) (or Fe (iron)) is grown on both sides of the striped waveguide by a selective growth method. .

Thereafter, the selective growth mask is removed, and then the contact layer 106 is etched obliquely with respect to the waveguide for separation between the regions. The contact layer 106 is removed, Si ions are implanted into the exposed portion of the p-type InP upper cladding layer 104, and annealed at 650 ° C. for 5 minutes to form n-type InP. Subsequently, a SiO ₂ insulating film 109 is formed, and a hole 109 a is formed in a portion corresponding to the current Ia or It injection portion of the insulating film 109 on the active waveguide layer 102 and the inactive waveguide layer 103. Then, the electrode is formed by lift-off.

  The semiconductor growth method is not limited to the metal organic vapor phase epitaxial growth method, and a molecular beam epitaxial growth method or other means may be used. The method of forming the diffraction grating is not limited to the electron beam exposure method, and a two-bundle interference exposure method or other means may be used.

  In addition, as a method of etching part of the contact layer 106 and the upper cladding layer 104, the active waveguide layer 102 and the inactive waveguide layer 103 are short in length and short in repetition period. Although an etching method with a small amount of side etching such as dry etching is desirable, there is no problem even with a method using wet etching or the like.

  The ion species used when the p-type is inverted to the n-type by ion implantation may be other ions such as C (carbon) and S (sulfur) instead of Si (silicon). In this embodiment, since an n-type semiconductor substrate is used, p-type InP is used for the clad and it is necessary to invert the p-type to the n-type. In the case of the n-type InP clad, Conversely, it is necessary to invert the n-type to the p-type, and Be (beryllium), Mg (magnesium), or the like may be implanted.

  As a material to be doped for the semi-insulator 122, Fe (iron) is generally used. However, by using Ru (ruthenium), it is possible to use Zn (zinc) which is a p-type InP dopant. Interdiffusion can be suppressed. Further, by using Ru, the capacitance is reduced as compared with the current block layer made of p-type and n-type semiconductors, so that the modulation characteristics can be improved. Thereby, the modulation characteristic could be improved to 10 GHz or more.

  In the present embodiment, the structure in which the active waveguide layer 102 and the inactive waveguide layer 103 are alternately and periodically described has been described as an example. Therefore, the active waveguide layer is not limited to the combination of the active waveguide layer 102 and the inactive waveguide layer 103 shown in FIG. The present invention can be applied even when the waveguide is divided into a plurality of regions and electrodes are provided.

  As described in this embodiment, the influence of leakage current appears remarkably when one element has a plurality of regions, but even when there are only two regions, the leakage current flowing between them is suppressed. In addition, this embodiment that can suppress the reflection of the guided light is useful.

  In this embodiment, the distributed active DFB laser has been described as an example. However, the present invention is not limited to these. For example, the present invention is also applicable to a laser electrode and a modulator electrode in a device in which a laser and a modulator are integrated. Is possible. That is, it can be applied to separation between different waveguide elements connected in series.

  The operations and effects of this embodiment are substantially the same as those of the first embodiment described above, and duplicate descriptions are omitted.

  A third embodiment of the present invention will be described in detail with reference to FIG.

  FIG. 7A is a top view of the semiconductor laser according to the present embodiment, FIG. 7B is an xx ′ cross-sectional view shown in FIG. 7A, and FIG. 7C is the present embodiment. FIG. 7D is a top view of the semiconductor laser according to the present embodiment with the electrodes and the insulating film removed, and FIG. 7E is a top view of the semiconductor laser according to the present embodiment. It is yy 'sectional drawing of Fig.7 (a).

  As shown in FIG. 7, the semiconductor laser according to the present example has an optical waveguide having a higher optical refractive index than the lower cladding 201 on the lower cladding (semiconductor substrate) 201 which is the first cladding layer made of n-type InP. Each layer includes one or more layers 215 and an upper clad 204 which is a second clad layer having a refractive index smaller than that of the optical waveguide layer 215.

  The optical waveguide layer 215 includes an active waveguide layer 202 and an inactive waveguide layer 203 that are alternately and periodically coupled in series along the light propagation direction. The active waveguide layer 202 has an optical gain with respect to light in the oscillation wavelength band, and is an active region having a length La made of GaInAsP. The inactive waveguide layer 203 is an inactive region having a length Lt made of GaInAsP having no optical gain and having a composition different from that of the active waveguide layer 202, and is a wavelength control region. In this example, the region lengths La and Lt were 22.3 μm and 44.7 μm, respectively, and the repetition period L (= La + Lt) of the active waveguide layer 202 and the inactive waveguide layer 203 was 67 μm.

  An upper clad 204 made of p-type InP is formed on the active waveguide layer 202 and the non-active waveguide layer 203, and a light propagation direction (hereinafter referred to as a light guide) is formed between the optical waveguide layer 215 and the upper clad 204. A diffraction grating 205 is formed in which concaves and convexes are formed at the same period over the entire length and the equivalent refractive index of the optical waveguide layer 215 is periodically modulated. In this example, the diffraction grating period was 241 nm in order to obtain an oscillation wavelength of 1.55 μm.

  On the upper clad 204, a contact layer 206 having a highly doped p-type InGaAsP and / or InGaAs multilayer structure for ohmic contact between the active waveguide layer 202 and the non-active waveguide layer 203 is provided. An active layer electrode 207 and a wavelength control electrode 208 are provided thereon so as to correspond to the active waveguide layer 202 and the inactive waveguide layer 203, respectively. A common electrode 210 is provided below the lower clad 201. Between the active region and the non-active region, ion implantation is performed on the contact layer 206 and part of the upper cladding 204.

  When GaInAsP having a band gap wavelength of 1.55 μm is used for the active waveguide layer 202, a laser having a band gap wavelength shorter than that, for example, GaInAsP having a band gap wavelength of 1.4 μm, is used for the inactive waveguide layer 203. Since it does not contribute to the oscillation gain, the carrier density is not constant. Thereby, the refractive index can be changed greatly by current injection.

  The active waveguide layer 202 and the inactive waveguide layer 203 do not have to be a bulk material. For example, a quantum well structure, a multilayer quantum well structure in which a quantum well is sandwiched between barrier layers, a quantum wire, a quantum dot, or the like Further, it may have a low-dimensional quantum well structure. In order to enhance light confinement and carrier confinement in the active layer, a separate confinement heterostructure (SCH) that introduces a layer having an intermediate refractive index between the active layer and the cladding layer may be introduced.

  The semiconductor used for this element is not limited to the combination of InP and GaInAsP, and may be another semiconductor such as GaAs, GaInNAs, AlGaInAs, InAs, and GaInNAs, and the band of the active waveguide layer and the inactive waveguide layer. The combination of gap wavelengths is not limited to the above.

  As shown in FIG. 7A, the active layer electrodes 207 and the wavelength control electrodes 208 are independently arranged. For example, if the active layer electrodes 207 and the wavelength control electrodes 208 are short-circuited by wires or the like outside the device, the same operation as in the first embodiment can be obtained. As shown in FIG. 7B, an insulating film 209 is formed under the active layer electrode 207 and the wavelength control electrode 208. In the insulating film 209, holes 209a are formed as electrode windows as shown in FIG. 7C at portions corresponding to the active region and the inactive region immediately above the waveguide (in FIG. ), The contact layer 206 is exposed. In other words, the optical waveguide layer 215 formed along the waveguide direction is located under the hole 209a. Further, below the insulating film 209, the contact layer 206 is provided only on the waveguide in each region, and is sandwiched between dielectrics 223 such as polyimide. And each area | region is electrically isolate | separated in the area | region which reversed the conductivity type of the semiconductor by ion implantation.

  All the active layer electrodes 207 and the wavelength control electrodes 208 are disposed independently. By configuring the active layer electrodes 207 and the wavelength control electrodes 208 to be short-circuited outside the device by, for example, a wire or the like, the same operation as in the first embodiment of the present invention described above can be obtained. A common electrode 210 is formed at the bottom of the substrate, that is, below the lower clad 201.

  As shown in FIG. 7D, an ion implantation region 216 having an angle with respect to the waveguide is formed between the regions so as to separate the contact layer 206 on the waveguide. Thereby, since the conductivity type of the semiconductor changes only in the ion-implanted region 216, for example, a region from one electrode to an adjacent electrode becomes p-type, n-type, and p-type, and current does not easily flow. The ion implantation region 216 may be ion-implanted while leaving the contact layer 206, but the effect is noticeable by performing ion implantation after removing the contact layer 206 having a high doping concentration.

  Further, as shown in FIG. 7E, a ridge structure in which polyimide is embedded as dielectric 223 on both sides of the upper clad 204 is formed. As a result, current is efficiently injected into the active waveguide layer 202 or the inactive waveguide layer 203. In this embodiment, the width of the waveguide, that is, the ridge width Ws is 2.5 μm.

  As shown in FIG. 7C, after the contact layer 206, the dielectric 223, and the ion implantation region 216 are covered with the insulating film 209, the hole 209a is formed only in the insulating film 209 corresponding to the current Ia or It implanted portion. It is formed (8 places in FIG. 7). The shape of the hole 209a is usually a rectangle. Even if the shape is rectangular, the effect of the present invention can be obtained, but the manufacturing process can be facilitated by using the same parallelogram as the shape of the contact layer 206. In other words, as shown in FIG. 7E, a step is formed on the surface of the substrate where the contact layer 206 is convex, and a pattern for punching the insulating film 209 with a photoresist is formed here. It becomes. The resist thickness of the step portion is not necessarily uniform, and the thickness is often smoothly changed according to the distance from the step. By matching the shape of the contact layer 206 with the shape of the hole, the hole pattern has a constant distance from the step, so that the pattern can be formed uniformly.

  As shown in FIG. 7A, the electrode patterns of the active layer electrode 207 and the wavelength control electrode 208 also reflect the shapes of the contact layer 206 and the insulating film 209, and the plane intersecting the waveguide direction is in the waveguide direction. Wiring is performed so as to incline with respect to the orthogonal direction. Similarly to the hole 209a, the active layer electrode 207 and the wavelength control electrode 208 may be drawn out in a direction perpendicular to the waveguide direction, but the electrode pattern is also formed by lift-on using a photoresist or wet etching. It is desirable to perform wiring so that the influence of the step is reduced as much as possible.

  Next, an example of a manufacturing method of the distributed active DFB laser according to the present embodiment will be described.

First, an active waveguide layer 202 is formed on the lower clad 201 made of n-type InP by metal organic vapor phase epitaxy. Next, a part of the active waveguide layer 202 is etched using SiO ₂ or SiN as a mask. The inactive waveguide layer 203 is produced by a selective growth method using the etching mask as it is. Thereafter, a diffraction grating pattern is formed on the applied resist by using an electron beam exposure method, and the semiconductor is etched using this as a mask to form a diffraction grating 205.

After re-growth of the upper clad 204 made of p-type InP and the contact layer 206 made of GaInAs by metal organic vapor phase epitaxy, a stripe shape having a width of 2.5 μm using SiO ₂ or SiN as a mask in order to suppress the transverse mode. The waveguide is processed. In this embodiment, the ridge is formed by wet etching using a resist as a mask. However, the ridge may be formed by dry etching using SiO ₂ or SiN as a mask.

Thereafter, a SiO ₂ or SiN film is formed, and a pattern of the separation groove 214 is formed only on the ridge using a thick resist. Next, the contact layer 206 is obliquely etched for separation between the regions, Si ions are implanted, and annealing is performed at 700 degrees for 10 minutes to form n-type InP.

Subsequently, polyimide is embedded in the side of the ridge and in the separation groove 214 and solidified in an oven of 350 degrees, and then a SiO ₂ insulating film 209 is formed, and on the active waveguide layer 202 and the inactive waveguide layer 203. A hole is made in the insulating film 209. An electrode pattern is formed by lift-off so that the active layer electrodes 202 and the non-active layer electrodes 203 are short-circuited on the element.

  The semiconductor growth method is not limited to the metal organic vapor phase epitaxial growth method, and a molecular beam epitaxial growth method or other means may be used. The method of forming the diffraction grating is not limited to the electron beam exposure method, and a two-bundle interference exposure method or other means may be used.

  In addition, as a method of etching part of the contact layer 206 and the upper cladding layer 204, the active waveguide layer 202 and the inactive waveguide layer 203 are short in length and have a short repetition period. Although an etching method with a small amount of side etching such as dry etching is desirable, there is no problem even with a method using wet etching or the like.

  The ion species used when the p-type is inverted to the n-type by ion implantation may be other ions such as C (carbon) and S (sulfur) instead of Si (silicon). In this embodiment, since an n-type semiconductor substrate is used, p-type InP is used for the clad and it is necessary to invert the p-type to the n-type. In the case of the n-type InP clad, Conversely, it is necessary to invert the n-type to the p-type, and Be (beryllium), Mg (magnesium), or the like may be implanted.

  In this embodiment, the dielectric 223 is used to reduce the capacity and protect the ridge structure, but both sides may be air. Moreover, although polyimide which is an organic material is used as the dielectric 223, other materials such as benzocyclobutene (BCB) may be used. By using the dielectric 223, the capacitance is reduced as compared with the current blocking layer, so that the modulation characteristics can be improved. In addition, the modulation characteristic can be improved to 10 GHz or more by suppressing the leakage current between the active region and the inactive region by the separation groove 214.

  In this embodiment, the structure in which the active waveguide layers 202 and the inactive waveguide layers 203 are alternately and periodically described has been described as an example. 7 is not limited to the combination of the active waveguide layer 202 and the inactive waveguide layer 203 shown in FIG. 7, and the active waveguide layer is divided into a plurality of regions or inactive. The present invention can be applied even when the waveguide is divided into a plurality of regions and electrodes are provided.

  As described in this embodiment, the influence of leakage current appears remarkably when one element has a plurality of regions, but even when there are only two regions, the leakage current flowing between them is suppressed. In addition, this embodiment that can suppress the reflection of the guided light is useful.

  In this embodiment, the distributed active DFB laser has been described as an example. However, the present invention is not limited to these. For example, the present invention is also applicable to a laser electrode and a modulator electrode in a device in which a laser and a modulator are integrated. Is possible. That is, it can be applied to separation between different waveguide elements connected in series.

  The operations and effects of this embodiment are substantially the same as those of the first embodiment described above, and duplicate descriptions are omitted.

  A fourth embodiment of the present invention will be described in detail with reference to FIG.

  FIG. 8A is a top view of the semiconductor laser according to the present embodiment, FIG. 8B is an xx ′ cross-sectional view shown in FIG. 8A, and FIG. 8C is the present embodiment. FIG. 8D is a top view of the semiconductor laser according to the present embodiment with the electrodes and the insulating film removed, and FIG. 8E is a top view of the semiconductor laser according to the present embodiment. 8 is a cross-sectional view taken along the line yy ′ of FIG. 8, FIG. 9 is a top view showing another example of the semiconductor laser according to the present embodiment, and FIG. 10 is a graph showing the relationship between the upper clad thickness and the equivalent refractive index. is there.

  As shown in FIG. 8, the semiconductor laser according to the present example includes an optical waveguide layer 315 having an optical refractive index larger than that of the lower cladding 301 on the lower cladding (semiconductor substrate) 301 than the n-type InP, and the optical waveguide layer. One or more upper clads 304 each having a refractive index lower than 315 are included.

  The optical waveguide layer 315 includes an active waveguide layer 302 and an inactive waveguide layer 303 that are alternately and periodically coupled in series along the light propagation direction. The active waveguide layer 302 has an optical gain with respect to light in the oscillation wavelength band, and is an active region having a length La made of GaInAsP. The non-active waveguide layer 303 has no optical gain, and is a non-active region having a length Lt made of GaInAsP having a different composition from the active waveguide layer 302, and is a wavelength control region. In the present embodiment, the region lengths La and Lt are 29.5 μm, respectively, and the repetition period L (= La + Lt) of the active waveguide layer 302 and the inactive waveguide layer 303 is 59 μm.

  An upper clad 304 made of p-type InP is formed on the active waveguide layer 302 and the inactive waveguide layer 303, and a light propagation direction (hereinafter referred to as a light guide) is formed between the optical waveguide layer 315 and the upper clad 304. A diffraction grating 305 is formed in which irregularities are formed at the same period over the entire length and the equivalent refractive index of the optical waveguide layer 315 is periodically modulated. In this example, the diffraction grating period was set to 243 nm in order to obtain an oscillation wavelength of 1.55 μm.

  On the upper clad 304, a contact layer 306 having a multilayer structure of highly doped p-type InGaAsP and / or InGaAs is provided for ohmic contact between the active waveguide layer 302 and the inactive waveguide layer 303. An active layer electrode 307 and a wavelength control electrode 308 are provided thereon so as to correspond to the active waveguide layer 302 and the inactive waveguide layer 303, respectively.

  Between the active region and the non-active region, an electrode separation groove (hereinafter simply referred to as “separation groove”) 314 having a depth d = 2 μm and a width We = 5 μm is formed in part of the contact layer 306 and the upper cladding 304. It is formed (seven places in FIG. 8). The depth d of the separation groove 314 is a depth at which 0.5 μm of the upper clad 304 remains on the optical waveguide layer 315 after the separation groove 314 is formed.

  The position of the separation groove 314 can efficiently prevent leakage current between the mutual regions by providing the center of the boundary between the active region and the non-active region, but it is not necessarily centered on the boundary between the active region and the non-active region. The effect of the separation groove 314 can be obtained even if it is disposed at a position offset in either region. In the case of the distributed active DFB laser of this embodiment, a relatively large current is injected in the active region in order to generate a sufficient gain for obtaining a desired oscillation output, and in the wavelength control region (inactive region). The wavelength is controlled by a relatively small current.

  Therefore, the bias voltage of the inactive region is lower than that of the active region, and in many cases, leakage current flows from the active region to the inactive region. In this case, the effect of suppressing the leakage current can be enhanced by shifting the center of the isolation groove 314 to the active region side instead of disposing it at the connection portion between the active region and the inactive region.

Further, ion implantation is performed under the separation groove 314 (ion implantation region 316).

  All the active layer electrodes 307 and the wavelength control electrodes 308 are integrated with each other and are short-circuited on each other. A common electrode 310 is formed at the bottom of the substrate, that is, below the lower clad 301.

  When GaInAsP having a band gap wavelength of 1.55 μm is used for the active waveguide layer 302, a laser having a band gap wavelength shorter than that, for example, GaInAsP having a band gap wavelength of 1.4 μm, is used for the inactive waveguide layer 303. Since it does not contribute to the oscillation gain, the carrier density is not constant. Thereby, the refractive index can be changed greatly by current injection.

  The active waveguide layer 302 and the inactive waveguide layer 303 do not have to be a bulk material. For example, a quantum well structure, a multilayer quantum well structure in which a quantum well is sandwiched between barrier layers, a quantum wire, a quantum dot, or the like Further, it may have a low-dimensional quantum well structure. In order to enhance light confinement and carrier confinement in the active layer, a separate confinement heterostructure (SCH) that introduces a layer having a refractive index between the active layer and the clad layer may be introduced.

  The semiconductor using this element is not limited to the combination of InP and GaInAsP, and may be another semiconductor such as GaAs, GaInNAs, AlGaInAs, InAs, and GaInNAs. The active waveguide layer 302 and the inactive waveguide layer 303 may be used. The combination of the band gap wavelengths is not limited to the above.

  As shown in FIG. 8A, the active electrodes 307 and the wavelength control electrodes 308 are integrated to form a comb shape. As shown in FIG. 8B, an insulating film 309 is formed under the active layer electrode 307 and the wavelength control electrode 308. A hole 309a as an electrode window as shown in FIG. 8C is formed in the insulating film 309 immediately above the waveguide and corresponding to the active region and the non-active region, and the contact layer 306 is exposed. It is supposed to be. In other words, the optical waveguide layer 315 formed along the waveguide direction is located under the hole 309a. Further, below the insulating film 309, contact is made along the waveguide direction as shown in FIGS. 8D and 8E so that the contact layer 306 is left only on the waveguide in each region. Etched at a depth d to leave layer 306.

  As shown in FIG. 8D, the contact layer 306 is formed in a parallelogram island shape. Thereby, a separation groove 314 that separates the contact layer 306 having an angle with respect to the waveguide direction is formed between the regions. A part of the upper clad 304 made of InP below the contact layer 306 is also etched, and ion implantation is performed below the isolation groove 314 to form an ion implantation region 316. This increases the ionization polarization resistance.

  Furthermore, as shown in FIG. 8E, p-type semiconductors 311 and n-type semiconductors 312 made of InP are alternately formed as current blocking layers 313 on both sides of the optical waveguide layer 315 having a width Ws, and buried heterostructures ( BH). Thereby, current is efficiently injected into the active waveguide layer 302 or the inactive waveguide layer 303. In this embodiment, the current blocking layer 313 is realized by combining p-type InP and n-type InP. However, semi-insulating InP doped with Fe (iron), Ru (ruthenium), or the like may be used. In this embodiment, the waveguide width Ws is 1.3 μm.

  The length of the separation groove 314 in the direction perpendicular to the waveguide corresponds to the width Wa of the contact layer 306 and needs to be set longer than at least the waveguide width Ws = 1.3 μm. There is no major problem caused by the fact that the width Wa is longer than the width Ws of the waveguide. In this embodiment, however, the contact resistance for injecting the current Ia or It into the optical waveguide layer 315 or a size that does not cause a problem when the electrode is routed. Therefore, the width Wa of the separation groove 314 is set to 4 μm.

  As shown in FIG. 8C, after the contact layer 306 and the upper clad 304 are covered with the insulating film 309, a hole 309a is formed only in the portion of the insulating film 309 corresponding to the current Ia or It injection portion (FIG. 8). Then 8 places). The shape of the hole 309a is usually a rectangle. Even if the shape is rectangular, the effect of the present invention can be obtained, but the manufacturing process is facilitated by using the same parallelogram as the shape of the contact layer 306. That is, as shown in FIG. 8E, a step is formed on the surface of the substrate where the contact layer 306 portion is convex, and a pattern for forming a hole in the insulating film 309 is formed using a photoresist. It becomes. The resist thickness of the step portion is not necessarily uniform, and the thickness is often smoothly changed according to the distance from the step. By matching the shape of the contact layer 306 with the shape of the hole, the hole pattern has a constant distance from the step, so that the pattern can be formed uniformly.

  As shown in FIG. 8A, the electrode patterns of the active layer electrode 307 and the wavelength control electrode 308 also reflect the shapes of the contact layer 306 and the insulating film 309, and the plane intersecting the waveguide direction is in the waveguide direction. Wiring is performed so as to incline with respect to the orthogonal direction. Similarly to the hole 309a, the active layer electrode 307 and the wavelength control electrode 308 may be drawn out in a direction perpendicular to the waveguide direction, but the electrode pattern is also formed by lift-on using a photoresist or wet etching. It is desirable to perform wiring so that the influence of the step is reduced as much as possible. Therefore, the shape shown in FIG. 9 may be used instead of the shape shown in FIG.

  Next, an example of a manufacturing method of the distributed active DFB laser according to the present embodiment will be described.

First, an active waveguide layer 302 is formed on the lower clad 301 made of n-type InP by metal organic vapor phase epitaxy. Next, a part of the active waveguide layer 302 is etched using SiO ₂ or SiN as a mask. Using the etching mask as it is, the inactive waveguide layer 303 is produced by a selective growth method. Thereafter, a diffraction grating pattern is formed on the applied resist using an electron beam exposure method, and the semiconductor is etched using this as a mask to form a diffraction grating 305.

After re-growing a part of the upper clad 304 made of p-type InP by metal organic vapor phase epitaxy, a waveguide is formed in a stripe shape having a width of 1.3 μm using SiO ₂ or SiN as a mask in order to suppress the transverse mode. Process. Using the etching mask as it is, an InP current blocking layer 313 made of the p-type semiconductor 311 / n-type semiconductor 312 is grown on both sides of the striped waveguide by a selective growth method.

Thereafter, the selective growth mask is removed, and the remaining InP upper clad layer 304 and GaInAs contact layer 306 are grown. Next, the contact layer 306 and part of the upper clad 304 are etched into a parallelogram island using a SiN mask. Thereafter, Si ions are implanted into portions other than the contact layer 306, and n-type InP is formed by annealing at 750 degrees for 1 minute. A SiO ₂ insulating film 309 is formed, and a hole 309a is opened in a portion corresponding to the current Ia or It injection portion of the insulating film 309 on the active waveguide layer 302 and the inactive waveguide layer 303. An electrode pattern is formed by lift-off so that the active layer electrodes 307 and the non-active layer electrodes 308 are short-circuited on the element.

  The semiconductor growth method is not limited to the metal organic vapor phase epitaxial growth method, and a molecular beam epitaxial growth method or other means may be used. The method of forming the diffraction grating is not limited to the electron beam exposure method, and a two-bundle interference exposure method or other means may be used.

  In addition, as a method of etching part of the contact layer 306 and the upper cladding layer 304, the active waveguide layer 302 and the inactive waveguide layer 303 are short and have a short repetition period. Although an etching method with a small amount of side etching such as dry etching is desirable, there is no problem even with a method using wet etching or the like.

  The ion species used when the p-type is inverted to the n-type by ion implantation may be other ions such as C (carbon) and S (sulfur) instead of Si (silicon). In this embodiment, since an n-type semiconductor substrate is used, p-type InP is used for the clad and it is necessary to invert the p-type to the n-type. In the case of the n-type InP clad, Conversely, it is necessary to invert the n-type to the p-type, and Be (beryllium), Mg (magnesium), or the like may be implanted.

  In this embodiment, ion implantation is performed after the separation groove 314 is formed. In the ion implantation, normally, channeling is avoided, and ions are incident at an angle of about 7 degrees from the substrate surface. For this reason, depending on the shape of the separation groove 314, ions cannot be appropriately incident on the lower portion of the separation groove 314. Therefore, the separation groove may be formed after ion implantation.

  In this embodiment, the structure in which the active waveguide layers 302 and the inactive waveguide layers 303 are alternately and periodically described has been described as an example. Therefore, the active waveguide layer is not limited to the combination of the active waveguide layer 302 and the inactive waveguide layer 303, and the active waveguide layer is divided into a plurality of regions, or the inactive waveguide is divided into a plurality of inactive waveguide layers. The present invention can be applied even when the electrodes are provided by being divided into regions.

  As described in this embodiment, the influence of leakage current appears remarkably when one element has a plurality of regions, but even when there are only two regions, the leakage current flowing between them is suppressed. In addition, this embodiment that can suppress the reflection of the guided light is useful.

  In this embodiment, since the application example to the distributed active DFB laser is shown, the electrode 307 on the active waveguide layer 302 and the electrode 308 on the inactive waveguide layer 303 are each short-circuited on the element. Although described, the present invention can be applied even if each electrode is independent. Further, even if it is not a distributed active DFB laser, for example, it can be applied to an electrode of a laser part and an electrode part of a modulator in a device in which a laser and a modulator are integrated. That is, it can be applied to separation between different waveguide elements connected in series.

  Subsequently, the operation of the present embodiment will be described.

  In order to electrically separate the regions, it is certain to form a separation groove to physically cut off the current path. However, since the separation groove is made of a material other than a semiconductor such as air or a dielectric, the refractive index is greatly different from that of a semiconductor.

  Here, FIG. 10 shows the relationship between the upper cladding thickness and the equivalent refractive index in the case of a semiconductor substrate composed of eight active layers and SHC layers that emit light at 1.55 μm. By forming the separation groove 314 between the regions as in the present embodiment, the thickness of the upper clad located below the separation groove 314 (hereinafter referred to as the upper clad thickness of the separation groove portion) is reduced, and the equivalent refractive index. Decreases. Although it depends on the field distribution of light propagating in the waveguide, it can be seen from FIG. 10 that in this example, the equivalent refractive index rapidly decreases when the thickness of the upper cladding of the separation groove is less than about 1000 nm.

  For example, if the upper cladding thickness of the separation groove is 2000 nm, the equivalent refractive index is 3.1978, but if the upper cladding thickness of the separation groove is 1500 nm, the equivalent refractive index is 3.1977, and the upper cladding thickness of the separation groove is Is 1000 nm, the equivalent refractive index is 3.1974, and the equivalent refractive index is reduced by 0.0004 compared to when the upper cladding thickness of the separation groove is 2000 nm. Further, when the upper cladding thickness of the separation groove is 500 nm, the equivalent refractive index is further reduced to 3.1941, and the equivalent refractive index is decreased by 0.0037 compared to the case where the upper cladding thickness of the separation groove is 2000 nm. . Therefore, when the separation groove 314 is deep, reflection is increased.

  On the other hand, in the method of making it difficult for electricity to flow by forming a pnp junction by ion implantation, the amount of change in the refractive index is smaller than that of the separation groove 314, but electricity becomes easier to flow than the separation groove 314.

  Therefore, in this embodiment, the separation groove 314 is used in a region where the reflection is not so large, and the separation between the electrodes is improved in the region where the reflection due to the separation groove is large, thereby improving the separation between the electrodes. Reduce.

  Further, as described in the first to third embodiments, if the separation groove is formed obliquely with respect to the waveguide, the influence of reflection due to the refractive index difference can be further reduced.

  In this embodiment, the action and effect obtained by inclining the separation groove 314 and the ion implantation region 316 from the waveguide are substantially the same as those in the first embodiment described above, and redundant description is omitted.

  A fifth embodiment of the present invention will be described in detail with reference to FIG.

  FIG. 11A is a top view of the semiconductor laser according to the present embodiment, FIG. 11B is a top view of the semiconductor laser according to the present embodiment with the electrodes removed, and FIG. It is a top view of the state which removed the electrode and insulating film of the semiconductor laser which concerns on a present Example.

  In the present embodiment, for example, the shapes of the active layer electrode 307, the wavelength control electrode 308, the hole 309a formed in the insulating film 309, and the separation groove 314 described in the fourth embodiment are changed. . Other configurations are generally the same, and redundant description is omitted. In FIG. 11, 404 is an upper clad, 406 is a contact layer, 407 is an active layer electrode, 408 is a wavelength control electrode, 409 is an insulating film, and 409 a is a hole formed in the insulating film 409.

  In Examples 1 to 4 described above, in order to suppress the reflection of light at the refractive index boundary surface, the ion implantation region is arranged in the waveguide direction for the purpose of inclining the refractive index boundary surface with respect to the waveguide direction. It was provided so as to be inclined with respect to a direction orthogonal to the direction. However, if all the ion implantation regions are inclined at the same angle with respect to the direction orthogonal to the waveguide direction, resonance may occur.

  Therefore, in this embodiment, as shown in FIG. 11C, the adjacent contact layers 406 are configured to have different inclinations. Thereby, even when reflection occurs in the ion implantation region, resonance can be suppressed.

  In FIG. 11, the separation groove and the ion-implanted surface are formed so that the inclination angle with respect to the waveguide direction is symmetric with respect to the plane orthogonal to the waveguide direction, and the inclination angles are alternately made equal. However, in order to suppress resonance, it is most preferable that the angles of inclination of the separation grooves or the ion implantation regions are all different. However, as long as the separation grooves are located at some distance, there is no problem even if they have the same inclination angle.

In the simplest case, separation grooves or ion implantation regions having the same inclination angle only need to be intermittently arranged. Therefore, the width of the separation groove or ion implantation region in the direction perpendicular to the waveguide direction is d, and the waveguide When the angle of the separation groove or the ion implantation region with respect to the direction is θ, the distance x between the separation grooves or the ion implantation regions having the same inclination angle satisfies the relationship of the following expression (10), thereby resonating. Can be suppressed.
x> 2d / sin (2θ) (10)

  Further, as in the present embodiment, the active layer electrodes 407 and the wavelength control electrodes 408 are integrated with each other by alternately reversing the inclination angle of the separation groove or the boundary surface of the ion implantation region. When the electrodes 407 and 408 are pulled out, as shown in FIG. 11A, the width of the leading portions 407a and 408a can be formed wider than in the case of the first to fourth embodiments. Can be easily.

  A sixth embodiment of the present invention will be described in detail with reference to FIG.

  12A is a top view of the semiconductor laser according to the present embodiment, FIG. 12B is a cross-sectional view taken along line xx ′ shown in FIG. 12A, and FIG. 12C is the present embodiment. FIG. 12D is a top view of the semiconductor laser according to the present embodiment with the electrode and insulating film removed, and FIG. 12E is a top view of the semiconductor laser according to the present embodiment. It is yy 'sectional drawing of Fig.12 (a).

  In this embodiment, for example, the shapes of the active layer electrode 307, the wavelength control electrode 308, the hole 309a formed in the insulating film 309, the separation groove 314, and the ion implantation region 316 are different from those in the third embodiment. is there. Further, separation grooves are formed in the same manner as in Example 4 after ion implantation. When ion implantation is performed, although depending on the ion implantation energy and the number of ion implantations, the concentration of implanted impurities near the substrate surface becomes low. Usually, the ion concentration from the surface to a desired depth is made uniform by changing the ion implantation energy and performing multiple implantations. Therefore, by forming the separation groove after the ion implantation, the portion having a low impurity concentration on the surface is physically removed, and the effect that the number of ion implantations can be reduced can be obtained.

  Other configurations are generally the same, and redundant description is omitted. In FIG. 12, 501 is a lower clad, 502 is an active waveguide layer, 503 is an inactive waveguide layer, 504 is an upper clad, 505 is a diffraction grating, 506 is a contact layer, 507 is an active layer electrode, and 508 is a wavelength control electrode. 509 is an insulating film, 509a is a hole formed in the insulating film 509, 510 is a common electrode, 514 is a separation groove, 515 is an optical waveguide layer, 516 is an ion implantation region, and 523 is a dielectric.

  In the first to fourth embodiments described above, in order to suppress the reflection of light at the refractive index boundary surface, the separation groove is formed for the purpose of inclining the refractive index boundary surface with respect to the direction orthogonal to the waveguide direction. It provided so that it might incline at the same angle with respect to the direction orthogonal to the waveguide direction. However, if all the separation grooves are inclined at the same angle with respect to the waveguide direction, resonance may occur. Therefore, in the fifth embodiment, the inclination angle of the adjacent separation groove 414 is configured to be symmetric with respect to the plane orthogonal to the waveguide direction. As a result, even when reflection occurs in the separation groove 414, resonance can be suppressed. On the other hand, in this embodiment, in FIG. 12, the inclination angles of the separation grooves 514 with respect to the waveguide direction are all different.

  It should be noted that there is no problem even if the separation grooves 514 located at some distance from each other have the same inclination angle. In the simplest case, the separation grooves 514 having the same inclination angle only need to be intermittently arranged. Therefore, the width of the separation groove 514 in the direction orthogonal to the waveguide direction is d, and the direction perpendicular to the waveguide direction is When the angle of the separation groove 514 is θ, resonance can be suppressed by making the distance x between the separation grooves 514 having the same inclination angle satisfy the relationship of the above-described expression (10).

  Further, in this embodiment, as shown in FIG. 12A, the active layer electrode 507 and the wavelength control electrode 508 are formed so that the surfaces intersecting the waveguide direction are orthogonal to the waveguide direction. Yes. Accordingly, when the electrodes 507 and 508 are pulled out, the electrodes 507 and 508 are overlaid on the separation groove 514, so that the manufacturing process may be somewhat complicated. However, in the case where the inclination angles of the separation grooves 514 are all different, when all the electrodes 507 and 508 are made to coincide with the inclination angles of the separation grooves 514, the resistance varies due to the different electrode widths, and the current injection is uneven. There is a risk of becoming. Accordingly, as shown in FIG. 12A, the surfaces of the electrodes 507 and 508 that intersect the waveguide direction are formed so as to be orthogonal to the waveguide direction, and the shapes of the electrodes 507 and 508 can be kept constant. Is preferable.

  The present invention relates to a wavelength tunable semiconductor laser used as a light source for optical fiber communication and a light source for optical measurement. For example, the present invention relates to a light source for optical wavelength (frequency) multiplexing system in optical communication and a light source for optical measurement that covers a wideband wavelength band. Applicable.

It is explanatory drawing of the semiconductor laser which concerns on the 1st Example of this invention. It is a top view which shows the other example of the semiconductor laser which concerns on the 1st Example of this invention. It is explanatory drawing which shows the refractive index of the light in the interface of the substance from which a refractive index differs mutually. It is a graph which shows the relationship between a band gap wavelength and a refractive index difference. It is a graph which shows the coupling factor of the reflected wave with respect to the incident angle to a refractive index boundary. It is explanatory drawing of the semiconductor laser which concerns on the 2nd Example of this invention. It is explanatory drawing of the semiconductor laser which concerns on the 3rd Example of this invention. It is explanatory drawing of the semiconductor laser which concerns on the 4th Example of this invention. It is a top view which shows the other example of the semiconductor laser based on the 4th Example of this invention. It is a graph which shows the relationship between an upper clad thickness and an equivalent refractive index. It is explanatory drawing of the semiconductor laser which concerns on the 5th Example of this invention. It is explanatory drawing of the semiconductor laser which concerns on the 6th Example of this invention. It is explanatory drawing of the conventional distributed active DFB laser. It is sectional drawing of the other conventional distributed active DFB laser. It is sectional drawing of the other conventional distributed active DFB laser. It is sectional drawing of the other conventional distributed active DFB laser. It is sectional drawing of the other conventional distributed active DFB laser.

Explanation of symbols

1, 101, 201, 301, 501 Lower cladding 2, 102, 202, 302, 502 Active waveguide layer 3, 103, 203, 303, 503 Inactive waveguide layer 4, 104, 204, 304, 504 Upper cladding 5 , 105, 205, 305, 505 Diffraction grating 6, 106, 206, 306, 506 Contact layer 7, 107, 207, 307, 507 Active layer electrode 8, 108, 208, 308, 508 Inactive layer electrode 9, 109, 209, 309, 509 Insulating film 9a, 109a, 209a, 309a, 509a Hole 10, 110, 210, 310, 510 Common electrode 16, 116, 216, 316, 516 Ion implantation region 122 Semi-insulator 223, 523 Dielectric

Claims (12)

An optical waveguide including at least one first semiconductor cladding layer, an optical waveguide layer having a higher refractive index than that of the first semiconductor cladding layer, and a second semiconductor cladding layer having a lower refractive index than that of the optical waveguide layer. A semiconductor waveguide device coupled in series in two or more waveguide directions,
Electrodes for supplying current independently to the optical waveguides;
Provided between adjacent electrodes in the second semiconductor clad layer, and having a different conductivity type separation layer or insulating separation layer from the second semiconductor clad layer,
Normal of plane intersecting the waveguide direction of the separation layer, inclined by the inclination angle θ in pairs in the waveguide direction,
The gap x between adjacent separation layers satisfies x> 2d / sin (2 [theta]) when the inclination angles [theta] of adjacent separation layers are different from each other or the inclination angles [theta] of adjacent separation layers are equal. A semiconductor waveguide device. A semiconductor waveguide device according to claim 1, wherein
The isolation layer is formed by ion implantation or diffusion of impurities into the second semiconductor cladding layer. A semiconductor waveguide device according to claim 1 or 2, wherein
A semiconductor waveguide device, wherein a separation groove is provided between adjacent electrodes in the second semiconductor cladding layer. A semiconductor waveguide device according to any one of claims 1 to 3, wherein
A semiconductor waveguide element characterized in that a normal line of a surface intersecting the waveguide direction of the separation layer is inclined at least 5 degrees with respect to the waveguide direction. A semiconductor waveguide device according to any one of claims 1 to 3, wherein
A semiconductor waveguide element, wherein a normal line of a surface intersecting a waveguide direction of the separation layer is inclined at an angle of 20 degrees to 55 degrees with respect to the waveguide direction. A semiconductor waveguide device according to any one of claims 1 to 5, comprising:
A semiconductor waveguide element characterized in that all surfaces of the separation layer intersecting the waveguide direction have the same inclination angle with respect to the waveguide direction. A semiconductor waveguide device according to any one of claims 1 to 5, comprising:
The separation layer has an equal inclination angle every other plane intersecting the waveguide direction, and the separation layers adjacent along the waveguide direction are mutually symmetrical with respect to the plane perpendicular to the waveguide direction. A semiconductor waveguide device characterized in that there is a semiconductor waveguide device. A semiconductor waveguide device according to any one of claims 1 to 7 ,
The end of the hole formed in the insulating film provided on the upper surface of the second semiconductor cladding layer that intersects the waveguide direction, or the end of the electrode that intersects the waveguide direction, or both, Each of the semiconductor waveguide elements is formed in parallel to the corresponding separation layer. A semiconductor waveguide device according to any one of claims 1 to 8 , comprising:
The coupling surface of the optical waveguide layer has an inclination equal to that of the separation layer. A semiconductor waveguide device according to any one of claims 1 to 9 , wherein
A semiconductor waveguide device comprising a semi-insulating current blocking layer doped with ruthenium. Semiconductor laser characterized by using a semiconductor waveguide device as claimed in any one of claims 1 to 10. An optical waveguide including at least one first semiconductor cladding layer, an optical waveguide layer having an optical refractive index larger than that of the first semiconductor cladding layer, and a second semiconductor cladding layer having a refractive index lower than that of the optical waveguide layer. A method of manufacturing a semiconductor waveguide device in which two or more waveguides are coupled in series in the direction of an optical waveguide, and an electrode that supplies current independently to each of the optical waveguides is provided,
Impurities are ion-implanted or diffused between adjacent electrodes in the second semiconductor cladding layer, and have a conductivity type or insulation different from that of the second semiconductor cladding layer, and extend in a direction intersecting the waveguide direction. Forming a separation layer having an inclination with respect to a direction orthogonal to the waveguide direction ,
The normal of the surface intersecting the waveguide direction of the separation layer is inclined by an inclination angle θ with respect to the waveguide direction,
The gap x between adjacent separation layers satisfies x> 2d / sin (2 [theta]) when the inclination angles [theta] of adjacent separation layers are different from each other or the inclination angles [theta] of adjacent separation layers are equal. A method for producing a semiconductor waveguide device.

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