WO2005060058A1

WO2005060058A1 - Semiconductor laser and its manufacturing method

Info

Publication number: WO2005060058A1
Application number: PCT/JP2004/018703
Authority: WO
Inventors: Kiichi Hamamoto
Original assignee: Nec Corporation
Priority date: 2003-12-18
Filing date: 2004-12-15
Publication date: 2005-06-30
Also published as: JPWO2005060058A1

Abstract

A semiconductor laser having an active waveguide composed of a 1×1-MMI waveguide region (111) and single-mode waveguide regions (112, 113) connected to both ends of the 1×1-MMI waveguide region (111). A grating for selecting a single wavelength of the oscillated light propagated through the active waveguide is provided to the single-mode waveguide region (112).

Description

Specification

Semiconductor laser and method of manufacturing the same

Technical field

The present invention relates to a semiconductor laser, and more particularly to a dynamic multimode optical interference (active MMI) semiconductor laser and a method for manufacturing the same.

Background art

[0002] With the recent increase in communication demand, optical communication technology that enables high-speed, large-capacity communication is not only a basic system (meaning between metropolitan areas) but also a so-called metro system (meaning urban areas) and access. It has also been applied to areas such as systems (meaning between homes and buildings). Metro / access systems are expected to be used in large quantities (for example, the number of subscribers is expected to increase due to penetration of optical communication technologies such as “Fiber to the Home (FTTH)” into access systems). A transmission light source with low cost and low power consumption is required. On the other hand, transmission light sources with high light output performance are also required. For example, in the case of a metro system, realizing high light output performance eliminates the need to install a repeater along the transmission path, and allows the entire system to be constructed at low cost.

[0003] By the way, in an optical communication in which optical fiber transmission is performed, when a semiconductor laser having a plurality of oscillation wavelengths, for example, a Fabry-Perot semiconductor laser (FP-LD) is used as a transmission light source, an Chromatic dispersion occurs due to the difference in the propagation speeds, and high-speed signal communication cannot be performed. In order to avoid the influence of the chromatic dispersion of the optical fiber, a semiconductor laser capable of oscillating at a single wavelength (single axis mode) is usually used as a transmission light source.

[0004] As a semiconductor laser capable of oscillating at a single wavelength, a distributed feedback semiconductor laser (DFB-LD) is known. For example, non-patent literature (Govind P. Agrawal,

"Fiber-Optic Communication Systems, WILEY-INTERSCIENCE, p. 105, etc.) describes a DFB-LD in which a grating layer is provided near (directly under or directly above) a light-emitting layer (active layer). At present, DFB-LDs with low power consumption characteristics and high optical output performance required for transmission light sources in metro / access systems have not yet been realized. [0005] On the other hand, although it is an FP-LD, an active MMI type semiconductor laser has been proposed as a new laser diode capable of realizing low power consumption characteristics and high optical output performance by Hamamoto et al., The inventor of the present application. (See JP-A-11-68241). This active MMI semiconductor laser is a semiconductor laser that outputs single-mode light. An active waveguide including an active layer is composed of a 1X1-MMI waveguide and a pair of single-mode waveguides connected to both ends. (A single-mode waveguide designed to propagate only the fundamental mode). The 1X1_MMI waveguide is designed to perform “1X1 operation” based on the MMI theory. The following is a brief explanation of the MMI theory.

[0006] The MMI theory is known as a theory for designing a 1XN or NXN branching / merging passive optical waveguide (for example, "Lucas B. Soldano", "Journal of Lightware Technology" Ichi ", Vol. 13, No. 4, pp. 615-627, 1995). This MMI theory (the derived MMI length LTT is given by the following equation.

[0007] [number 1]

W _e -Wl + (scan ₀ ^{丌) (Nc / Nr) 2σ (} Nr'-Nc 2) 2

Here, L is the length of the MMI region, W1 is the width of the MMI region, Nr is the refractive index of the waveguide region, Nc is the refractive index of the cladding region, and λθ is the wavelength of the incident light. σ is “0” in the ΤΕ mode and “1” in the axis mode.

[0008] ΜΜΙAccording to theory,

[0009] [number 2]

When the condition of L = (3Z4 L, (N is a positive integer) is satisfied, the MMI region operates as a 1 XN optical waveguide.

[0010] [number 3] When L = (3 N) L, where N is a positive integer, the MMI region operates as an NXN optical waveguide. Based on this principle, it is possible to design a 1 × 1-MMI waveguide that becomes single mode light at both ends.

As described above, in an active MMI semiconductor laser in which a part of the active waveguide is composed of an MMI waveguide, the width of the waveguide can be increased (the area of the active layer can be increased). In addition, the element resistance can be reduced and low power consumption characteristics can be realized, as compared with an existing semiconductor laser having the same element length composed only of a single mode waveguide. For this reason, if an active MMI-type semiconductor laser can realize a structure capable of obtaining stable oscillation at a single wavelength, it is considered promising as a future transmission light source for metro / access systems.

As a semiconductor laser having an MMI waveguide and capable of oscillating at a single wavelength, for example, there is a semiconductor laser described in JP-A-2003-46190. In this semiconductor laser, an active region (light emitting region) is constituted only by the MMI waveguide, and a grating is provided in a passive region behind the active region. As another mode, Japanese Patent Application Laid-Open No. 2003-46190 describes a structure in which an external grating is provided behind an active region.

Disclosure of the invention

[0013] Problems to be solved by the invention are the following problems of the above-described conventional technology.

[0014] The DFB-LD described in the above non-patent document can oscillate at a single wavelength, but since the waveguide structure is formed of a narrow single-mode waveguide, There's a problem.

[0015] In order to reduce power consumption, it is necessary to reduce the element resistance to reduce the driving voltage. The device resistance can be reduced by increasing the area of the active layer (light-emitting layer). However, in a DFB-LD in which the waveguide structure is composed of a narrow single mode waveguide, It is difficult to increase the area of the active layer. It should be noted that increasing the element length reduces the element resistance S The force S that can be applied and an increase in the element length lead to a decrease in the element yield (production volume), which increases the cost. Thus, the DFB-LD has a problem that it cannot achieve the low power consumption characteristics and the high optical output performance required for the transmission light source of the metro / access system.

[0016] In the active MMI semiconductor laser described in Japanese Patent Application Laid-Open No. 11-68241, the area of the active layer can be increased, so that low power consumption characteristics and high light required for the transmission light source of the Metro Z access system are required. Output performance can be achieved, but there is a problem that stable oscillation at a single wavelength cannot be obtained.

[0017] In the active MMI semiconductor laser, it is conceivable to provide a grating near the active layer like a DFB-LD in order to perform single-wavelength oscillation. However, in a structure in which the main light emitting region is composed of an MMI waveguide, there are a plurality of different propagation modes in the MMI waveguide, so even if a grating is simply provided near the active layer, stable single-wavelength oscillation can be achieved. It is difficult to achieve.

In the semiconductor laser described in JP-A-2003-46190, a grating is provided in the passive waveguide region connected to the MMI waveguide, so that a passive region is newly integrated in addition to the active region for light emission. There is a need. For this reason, light loss in the passive region was unavoidable, and the structure was not suitable for increasing the output. It is necessary to form the passive region and the active region in the same device, which is disadvantageous in terms of cost reduction. The same problem occurs in the structure in which the external grating is provided.

An object of the present invention is to solve the above-mentioned problems, obtain low power consumption characteristics and high optical output performance required for a transmission light source of a metro / access system, and perform stable single-wavelength oscillation. It is to provide a semiconductor laser which can be used.

[0020] Another object of the present invention is to provide a method of manufacturing a semiconductor laser capable of manufacturing such a semiconductor laser at a high yield at low cost.

Another object of the present invention is to provide an optical communication module including such a semiconductor laser.

The semiconductor laser of the present invention is characterized in that at least one multimode interference waveguide In a semiconductor laser in which an active waveguide is composed of at least one single-mode waveguide connected to both ends or one end of a mode interference waveguide, the active waveguide is provided in a part of the active waveguide. It has a grating to select a single wavelength from the propagating oscillation light.

According to the above configuration, a single wavelength (single-axis mode) of the oscillating light propagating through the active waveguide is selected by the grating, so that stable laser oscillation at a single wavelength is possible. Therefore, by applying this structure, an active MM type semiconductor laser capable of single-wavelength oscillation can be realized.

In an active waveguide including a multi-mode interference waveguide, since the element resistance can be reduced by increasing the area of the active layer, the same element length consisting of only a single mode waveguide is used. Power consumption characteristics can be greatly improved compared to existing semiconductor lasers. Therefore, it is possible to achieve low power consumption characteristics required for the transmission light source of the Metro Z access system.

[0025] In addition, since the amount of heat generated by current injection generated in the active layer is reduced by reducing the element resistance, the kink of the DFB-LD (non-linearity in light output vs. operating current characteristics) is a cause. That is, the center wavelength shift of the active layer itself due to the current injection hardly occurs. For this reason, stable single-wavelength oscillation can be achieved even with a high injection current, thereby realizing high output characteristics.

[0026] In the above-described semiconductor laser of the present invention, the grating may be provided in the single-mode waveguide. According to this configuration, a single wavelength is selected in the single mode waveguide, and stimulated emission occurs even in the multimode interference waveguide for the selected single wavelength.

. Therefore, more stable high-output with single-wavelength oscillation is possible.

[0027] In addition, provided the grating multimode interference waveguide, may the grating width should be within ₂ times the width of the single-mode waveguide. According to this configuration, among a plurality of transverse modes propagating in the multimode interference waveguide, a single transverse mode can be reflected with respect to the center wavelength of the grating, thereby achieving stable single-wavelength operation. Is done. If the grating width exceeds twice the width of the single-mode waveguide, grating reflection occurs for each transverse mode propagating in the multi-mode interference waveguide, resulting in a stable reflection. It is relatively difficult to obtain single-wavelength oscillation.

[0028] Further, the grating may be provided over the entire length of the active waveguide, and a phase adjustment region may be provided in a portion of the grating located in the middle of the active waveguide. According to this configuration, the phase of the grating is inverted before and after the phase adjustment region, so that the gain difference between the single transverse mode selected by the grating and the other modes is sufficiently large. It becomes possible to take. Therefore, it is possible to realize a single wavelength oscillation at a high yield.

A feature of the optical communication module of the present invention is that any one of the semiconductor lasers described above and a circuit for driving the semiconductor laser are housed therein. By providing the semiconductor laser described above, an optical communication module having low power consumption characteristics and high light output performance required for a transmission light source of the Metro Z access system is realized.

[0030] The method for manufacturing a semiconductor laser according to the present invention includes a step of forming a grating region having a width wider than the width of the single mode waveguide in a region where the single mode waveguide is formed on the semiconductor substrate. And etching the formed grating region into the shape of an active waveguide. According to this manufacturing method, among the above-described semiconductor lasers of the present invention, a semiconductor laser having a structure in which a grating is provided in a single-mode waveguide can be manufactured with high yield and low cost.

[0031] Further, according to the method for manufacturing a semiconductor laser of the present invention, the width of the single-mode waveguide is not less than twice the width of the single-mode waveguide in the region where the active waveguide is formed on the semiconductor substrate. Forming a grating region having a width over the entire length of the active waveguide; and etching the formed grating region into the shape of the active waveguide. According to this manufacturing method, of the above-described semiconductor lasers of the present invention, it is possible to manufacture a semiconductor laser having a structure in which a grating is provided in a multimode interference waveguide at a low cost with good yield.

As described above, according to the present invention, an active MMI semiconductor laser capable of performing stable single-wavelength oscillation is realized, and low power consumption characteristics and high output required for the transmission light source of the Metro Z access system are achieved. The effect that characteristics can be achieved is produced.

[0033] The high output characteristics achieved by the calorie enable metro Z-access communication systems, especially In a mouth-to-mouth communication system, there is no need to install a repeater on the transmission path, and the entire system can be constructed at low cost.

Brief Description of Drawings

FIG. 1A is a schematic diagram when an active MMI semiconductor laser according to a first embodiment of the present invention is viewed from above.

FIG. 1B is a cross-sectional view taken along a dashed-dotted line Α_Α ′ in FIG. 1A.

FIG. 1C is a cross-sectional view taken along a dashed-dotted line Β—B ′ in FIG. 1A.

FIG. 2 is a schematic view showing a cross-sectional structure of an active layer of the active semiconductor laser shown in FIG. 1.

FIG. 3A is a diagram for explaining a manufacturing step of the active semiconductor laser shown in FIGS. 1A to 1C, and is a top view of a grating formation region.

FIG. 3D is a view for explaining the manufacturing step of the active semiconductor laser shown in FIGS. 1A-1C, and is a cross-sectional view after the MO-VPE step.

FIG. 3C is a view for explaining the manufacturing step of the active semiconductor laser shown in FIGS. 1A to 1C, and is a top view after the formation of a mask for forming a mesa.

FIG. 3D is a view for explaining the manufacturing step of the active semiconductor laser shown in FIGS. 1A-1C, and is a cross-sectional view after the mesa is manufactured.

FIG. 3A is a view for explaining the manufacturing step of the active semiconductor laser shown in FIGS. 1A-1C, and is a cross-sectional view after the MO-VPE recrystallization growth step.

FIG. 3F is a view for explaining the manufacturing step of the active semiconductor laser shown in FIGS. 1A-1C, and is a cross-sectional view after electrodes are formed.

FIG. 4Α is a schematic diagram of an active type semiconductor laser according to a second embodiment of the present invention when viewed from above.

FIG. 4Β is a cross-sectional view taken along a dashed-dotted line Α_Α ′ in FIG. 4Α.

FIG. 4C is a sectional view taken along dashed-dotted line Β—B ′ in FIG. 4Α.

FIG. 5 is a schematic diagram for explaining the grating region width of the active semiconductor laser shown in FIGS. 4A to 4C.

[FIG. 6I] A third embodiment of the active を semiconductor laser according to the present invention It is a schematic diagram when it sees.

FIG. 6B is a sectional view taken along dashed line AA ′ of FIG. 6A.

FIG. 6C is a sectional view taken along dashed line BB ′ in FIG. 6A.

FIG. 7A is a schematic diagram for explaining a grating region width of the active MMI type semiconductor laser shown in FIG. 6C.

Explanation of symbols

[0035] 101 n-InP semiconductor substrate

102 n-InGaAsP guide layer

103 n-InP cladding layer

104 Active layer

105 p-InP cladding layer

106 p-InP cladding layer

107 p-InGaAs contact layer

108 InGaAsP-SCH layer

109 InGaAsP / InGaAsP-MQW layer

111 lxl-MMI waveguide region

112-114 Single mode waveguide region

120 grating

121 λ / 4 phase adjustment region

121 SiO film

131 p-InP current block layer

132 n-InP current block layer

135, 136 electrodes

BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)

FIG. 1A is a schematic diagram of an active MMI semiconductor laser according to a first embodiment of the present invention as viewed from above. This active MMI semiconductor laser includes an active layer. The active waveguide structure includes a 1 × 1-MMI waveguide region 111 and a pair of single mode waveguide regions 112 and 113 provided at both ends thereof.

[0038] An end face of the single mode waveguide area 112 opposite to the side connected to the 1X1-MMI waveguide area 111 is a front end face of the element (hereinafter, simply referred to as a front end face), The laser light is emitted from here. An antireflection film is provided on the front end face (cleavage face). On the other hand, the end surface of the single mode mode waveguide region 113 opposite to the side connected to the 1 × 1-MMI waveguide region 111 is an end surface on the rear side of the element (hereinafter, simply referred to as a rear end surface). A high reflection film is provided on the rear end face. The front end face provided with the anti-reflection film and the rear end face provided with the high reflection film constitute reflectors before and after the laser resonator. The element length is about 600 zm, the length of the single mode waveguide region 112 is about 300 × m, and the length of the 11 1 1 1 waveguide region 111 is about 230 111. The waveguide width of the 1 × 1-MMI waveguide region 111 is about 9 zm, and the waveguide widths of the single-mode waveguide regions 112 and 113 are both about 2 μm.

FIG. 1B schematically shows a cross-sectional structure taken along a dashed line AA ′ of FIG. 1A. This cross section is obtained by cutting the single mode waveguide region 112 in a direction intersecting the longitudinal direction of the device. The waveguide portion of the single mode mode waveguide region 112 is formed on an n-InP semiconductor substrate 101 by forming an n-InGaAsP guide layer 102, an n-InP cladding layer 103, an active layer (light emitting layer) 104, and a p-InP cladding layer 105. A current block layer in which a p-InP current block layer 131 and an n-InP current block layer 132 are sequentially stacked is formed on both sides of the mesa structure. Is formed. The active layer 104 has an existing structure that is well known for semiconductor lasers. For example, as shown in FIG.

The structure is such that an InGaAsP / InGaAsP-MQW (multiple quantum well) layer 109 is sandwiched between InGaAsP-SCH (separated confinement heterostructure) layers 108 from above and below. On the face of the upper layer of the upper layer and the current blocking layer of the mesa structure, _P _inp cladding layer 106, p-InGaAs contact layer 107, electrodes 135 are sequentially stacked. On the back surface of the n-InP semiconductor substrate 101, an electrode 136 is formed.

FIG. 1C schematically shows a cross-sectional structure taken along a dashed-dotted line Β_Β ′ in FIG. 1A. This cross section is composed of the 1 × 1-MMI waveguide region 111 and the waveguide portions of the single mode waveguide regions 112 and 113. It is cut along the longitudinal direction of the child. In the waveguide portion of the single mode waveguide region 112, a grating 120 having periodic irregularities is formed at the interface between the n-InP semiconductor substrate 101 and the n-InGaAsP guide layer 102 over the longitudinal direction. The normalized coupling constant (kL) by the grating 120 is about 2. On the other hand, in the waveguide portion of the 1 × 1-MMI waveguide region 111 and the single mode waveguide region 113, the power grating 120 having the same laminated structure as the single mode waveguide region 112 is not formed.

In the active MMI semiconductor laser according to the present embodiment configured as described above, by applying a predetermined bias voltage between the electrodes 135 and 136, the mesa structure limited by the current blocking layer is applied. A current flows through the active layer 104 at the center of the portion. If the current is less than the threshold current, spontaneous emission and absorption occur. If the current exceeds the threshold current (the stimulated emission exceeds the absorption), the laser is ready for oscillation.

When laser oscillation is possible, the light amplified by stimulated emission is, according to the MMI theory, a force that propagates as multi-mode light in the 1 × 1-MMI waveguide region 111. In the waveguide regions 112 and 113, the light propagates as single mode light. During the process in which the single-mode light propagates through the single-mode waveguide region 112, a single wavelength is selected by the grating 120, and one laser oscillates at the selected single wavelength. The selected single wavelength is a wavelength at which the reflectance at the grating 120 is maximized, and can be arbitrarily set by adjusting the interval between the gratings 120.

A part of the laser light oscillated at a single wavelength propagates in the rear 1 × 1—MMI waveguide region 111, further propagates in the single mode waveguide region 113 behind it, and reaches the rear end face. To reach. The single-mode light having the single wavelength that has reached the rear end face is reflected there, propagates again in the single-mode waveguide region 113 and the 1 × 1 MMI waveguide region 111, and then enters the single-mode waveguide region 112. It reaches and is emitted as laser light from the front end face. During this propagation process, the single-wavelength light selected by the single-mode waveguide 112 undergoes stimulated emission even in the 1 × 1 MMI waveguide region 111, so that stable laser oscillation at a single wavelength is achieved. Operation is realized.

In addition, since the active waveguide has a structure including the 1 × 1-MMI waveguide region 111, the following advantages are provided in addition to the above features. (1) Since the element resistance can be reduced by increasing the waveguide width (enlarging the area of the active layer), the existing half of the same element length composed of only a single mode waveguide can be used. It has excellent low power consumption characteristics as compared to the semiconductor laser.

(2) Since the center wavelength shift of the active layer itself due to current injection, which is a cause of kink (non-linearity in optical output-operating current characteristics) of a normal DFB-LD, is unlikely to occur, a high injection current is obtained. , Stable single wavelength oscillation can be achieved, and high output characteristics can be realized.

[0047] The advantage of the above (2) will be briefly described. Normally, in the active layer, the refractive index changes due to heat generated by current injection, and the center wavelength shifts due to the change in the refractive index. According to the waveguide structure including the 1 X 1-M Ml waveguide region 111, the amount of heat generation is reduced by increasing the area of the active layer and decreasing the electric resistance, and as a result, the shift amount of the center wavelength is relatively reduced. It becomes smaller.

In the embodiment, since it is not necessary to integrate the passive waveguide region with the grating and the external grating region, it is possible to produce a semiconductor laser with good yield at low cost.

Next, a method of manufacturing the above-described active MMI semiconductor laser of the present embodiment will be described. FIGS. 3A to 3F show a series of manufacturing steps of the active MMI semiconductor laser shown in FIGS. 1A to 1C. FIGS. 3A and 3C are schematic views of the waveguide viewed from the upper surface side, and FIGS. 3B, 3D, and 3F are cross-sectional views of the waveguide (corresponding to the cross-section taken along a dashed line A-A 'in FIG. 1A). is there.

First, as shown in FIG. 3A, a grating 120 is formed on a part of the n-InP semiconductor substrate 101 by an electron beam exposure method and a usual wet etching method. The formation range of the grating 120 is a range including the single mode waveguide region 112, and the width thereof (in the width direction of the waveguide) is wider than the width of the single mode waveguide region 112.

Next, as shown in FIG. 3B, the n_InGaAsP guide layer 102 and n-InP are formed on the n-InP semiconductor substrate 101 on which the grating 120 is formed by metal organic chemical vapor deposition (MO-VPE). A cladding layer 103, an active layer 104, and a p_InP cladding layer 105 are sequentially formed. After that, as shown in Fig. 3C, a Si〇 film is deposited on the entire surface by thermal CVD, and a Si〇 mask 130 is formed by using ordinary photolithography and reactive ion etching (RIE). Form. This At this time, the SiO mask 130 is formed in a waveguide shape such that the single-mode waveguide region 112 is formed on the grating 120.

Next, as shown in FIG. 3D, a mesa is formed using an SiO mask 130 by an inductively coupled plasma (ICP) method. In the step of forming the mesa, the surface of the n-InP semiconductor substrate 101 is also etched, so that the region of the grating 120 coincides with the single mode waveguide region 112. After the formation of the mesa, as shown in FIG. 3E, a p-InP current blocking layer 131 and an n_InP current blocking layer 132 are formed around the mesa using the M〇VPE method, and the Si〇 mask remaining on the mesa is formed. 130 is removed using buffered hydrofluoric acid, and a p_InP cladding layer 106 and a p-InGaAs contact layer 107 are sequentially formed on the entire surface. Thereafter, as shown in FIG. 3F, an electrode 135 is formed on the upper surface by an electron beam evaporation method, and the back surface of the n-InP semiconductor substrate 101 is polished to form an electrode 136.

[0053] A plurality of laser elements are formed on the wafer in accordance with the above-described fabrication procedure of Figs. 3A and 3F. By cleaving along the boundary between the laser elements, a laser element having a structure as shown in FIGS. 1A to 1C is obtained. By this cleavage, the rear end face and the front end face of the laser element are respectively formed. Finally, an anti-reflection film is formed on the front end face and a high reflection film is formed on the rear end face, respectively, and the manufacture of the device is completed.

According to the above-described manufacturing process, the grating is directly provided in the active region, and the process of separately integrating the passive region as in a conventional semiconductor laser (see JP-A-2003-46190) is performed. Since it does not include it, it is possible to manufacture laser devices at low cost with good yield.

The waveguide structure and the method of manufacturing the same according to the present embodiment described above are merely examples, and the configuration and procedure thereof can be changed as appropriate. For example, in the manufacturing process described above, the force S using the M〇VPE method as the crystal growth method, and for example, a molecular beam growth method (MBE method) may be used instead. Also, the RIE method, which is not limited to the ICP method, can be applied to the mesa formation process.

Further, in the waveguide structure of the present embodiment, the grating 120 is provided on the surface of the n_InP semiconductor substrate 101 under the active layer 104, but the present invention is not limited to this structure. ,. If stable single wavelength oscillation can be obtained, grating 1 20 may be provided in another part. As a specific forming portion of the grating 120, for example,

a) Between n-InGaAsP guide layer 102 and n-InP cladding layer 103

b) Between the n-InP cladding layer 103 and the active layer 104

c) Between active layer 104 and p-InP cladding layer 105

d) Between p-InP cladding layer 106 and p-InGaAs contact layer 107

And the like. In addition, an n-InGaAs guide layer is provided between the p-InP clad layer 105 and the p-InP clad layer 106, and between the n-InGaAs guide layer and the p-InP clad layer 105 or the p-InP clad layer 106. It is also conceivable to provide a grating 120 in the structure.

The grating 120 may be formed over the entire length of the single mode waveguide region 112 or may be formed in a part of the single mode waveguide region 112.

Further, the grating 120 may be formed in the single mode waveguide region 113 instead of the single mode waveguide region 112, or may be formed in both the single mode waveguide regions 112 and 113. .

(Embodiment 2)

FIG. 4A is a schematic diagram when an active MMI semiconductor laser according to a second embodiment of the present invention is viewed from above. 4B is a cross-sectional view taken along a dashed-dotted line AA ′ in FIG. 4A, and FIG. 4C is a cross-sectional view taken along a dashed-dotted line Β_Β ′ in FIG. 4A.

As shown in FIGS. 4A to 4C, the active アクティブ semiconductor laser of the present embodiment also has an active waveguide including an active layer provided in a 1 × 1 − ΜΜΙ waveguide region 111 and at both ends thereof. The waveguide structure is basically the same as that of the first embodiment described above except that the formation portion of the grating 120 is different. Is the same as The element length is about 600 zm, and the single-mode waveguide areas 112 and 113 have a waveguide length of about Sl85 zm and a width of about 2 m. The length of the 1 × 1—MMI waveguide region 111 is about 230 μm, and the width is about 9 μm.

In the present embodiment, the grating 120 is formed on the surface of the n-InP semiconductor substrate 101 below the active layer 104, from the rear end face to the front end face. A λ Ζ4 phase adjustment region 121 is formed between the rear end surface and the front end surface of the grating 120. The phase adjustment region 121 is obtained by shifting the pitch of the grating 120 by / 4, and the phase of the grating 120 is inverted with the λ / 4 phase adjustment region 121 interposed therebetween. In the single mode waveguide regions 112 and 113, the width of the grating 120 is the same as the width of these waveguides (about 2 zm). In the 1 XI—MMI waveguide region 111, the single mode waveguide region 112 and It should be within twice (about 4 xm) the width of the 113 waveguide. Here, the width of the grating 120 is about 3 xm, and the normalized coupling constant (kL) is about 1. Note that an anti-reflection film is provided on both the rear end face and the front end face.

If a grating is provided in the 1 × 1 MMI waveguide region 111 without any restrictions, grating reflection usually occurs not only for the fundamental mode but also for higher-order modes, and therefore, stable Single wavelength oscillation cannot be obtained. From the experimental results by the present inventors so far, it has been found that since the propagation constants of the fundamental mode and the higher-order mode are different, single-wavelength oscillation cannot be obtained as a result. In the present embodiment, the grating 120 is formed at the waveguide center of the 1 × 1-MMI waveguide region 111, and the grating width is also the single-mode waveguides 112 and 113 (these are , Which is equivalent to a single transverse mode waveguide). According to this structure, among the transverse modes propagating in the 1 × 1-M Ml waveguide region 111, a single transverse mode can be reflected with respect to the grating center wavelength, so that it is stable. A single wavelength operation is realized.

Further, a λ / 4 phase adjustment region 121 is formed in the resonator, and the phase of the grating 120 is inverted with the / 4 phase adjustment region 121 interposed therebetween. Accordingly, it is possible to make the gain difference between the so-called main and sub-modes sufficiently large. Thus, single-wavelength oscillation with a high yield can be realized. Other advantages are the same as those of the first embodiment.

Next, a method for manufacturing the above-described active semiconductor laser of the present embodiment will be described.

The active も -type semiconductor laser of the present embodiment also basically has a method of forming the force grating 120 that can be manufactured by the steps shown in FIGS. 3A to 3F according to the first embodiment. This is different from the case (process in Fig. 3Α). That is, in the present embodiment, as shown in FIG. As described above, the grating 120 is formed on the surface of the n-InP semiconductor substrate 101 in the region where the active waveguide is formed, over the entire length of the active waveguide. The width A of the grating 120 is set to be equal to or more than the waveguide width B (same as the waveguide width of the single mode waveguide 113) of the single mode waveguide 112 to be formed in a later step and within twice the waveguide width B. . Here, the waveguide width B of the single mode waveguide 112 is about 2 zm, and the width A of the grating 120 is about 3 zm. However, considering the positional accuracy in the mesa forming process (the positional accuracy between the grating 120 and the single mode waveguides 112 and 113), it is desirable that the width A of the grating 120 be sufficiently larger than the waveguide width B.

After forming the grating 120, the steps shown in FIGS. 3B to 3F are performed. Then, the rear end face and the front end face of the laser element are formed by cleavage, and an antireflection film is formed on both end faces, thereby completing the manufacture of the element. Thus, a laser device having the structure shown in FIGS. 4A and 4C is obtained.

[0067] Also in the above manufacturing method, similarly to the manufacturing method in the above-described first embodiment, it is possible to manufacture a low-cost element with a good yield.

The above-described waveguide structure of the present embodiment and the method of manufacturing the same are merely examples, and the configuration and procedure thereof can be changed as appropriate. For example, in the manufacturing process described above,

Instead of the O-VPE method, for example, a molecular beam growth method (MBE method) can be used, or the RIE method can be used instead of the ICP method.

[0069] Further, the formation position of the grating 120 can be changed in a range where stable single-wavelength oscillation can be obtained. For example, the grating 120 may be provided at any of the positions a) to d) described in the first embodiment. Also, grating 120 is 1 X 1-M

It may be provided only in the Ml waveguide region 111.

(Embodiment 3)

FIG. 6A is a schematic diagram when an active MMI semiconductor laser according to a third embodiment of the present invention is viewed from above. FIG. 6B is a cross-sectional view taken along a dashed-dotted line A—A ′ in FIG.

FIG. 6C is a sectional view taken along dashed line BB ′ in FIG. 6A.

As shown in FIG. 6A and FIG. 6C, the active MMI semiconductor laser of the present embodiment has the 1 × 1-MMI waveguide region 111 in the structure of the second embodiment described above, One 1X1-MMI waveguide region llla, 111b is replaced by a single mode waveguide region 114 connecting these. The other parts are basically the same as those shown in FIGS. 4A to 4C. The element length is about 600 / im. The single-mode waveguide regions 112 and 113 both have a waveguide length of about 40 xm and a width of about 2 zm. Each of the lXl_MMI waveguide regions llla and 11 lb has a waveguide length of about 230 μm and a width of about 9 xm. The length of the single mode waveguide region 114 is about 60 × m and the width is about 2 μm.

The grating 120 is formed on the surface of the n_InP semiconductor substrate 101 under the active layer 104 and extends from the rear end face to the front end face. Have been. The λΖ4 phase adjustment region 121 is obtained by shifting the pitch of the grating 120 by λ / 4, and the phase of the grating 120 is inverted with the λ / 4 phase adjustment region 121 interposed therebetween. In the single mode waveguide regions 112 and 113, the width of the grating 120 is the same as the width of these waveguides (about 2 μΐη). In the 1 × 1 — waveguide region 111, the single mode waveguide region 112 The width is set to within twice (about 4 / im) the width of the waveguide of 113. Here, the width of the grating 120 is about 3 μΐη, and the normalized coupling constant (kL) is about 1. Note that an antireflection film is provided on both the rear end face and the front end face.

Also in the present embodiment, the grating 120 is formed at the center of the waveguide in the 1 × 1—MMI waveguide region llla, 1 lib, and the force of the grating is the same as that of the single mode waveguide 112 — The width is set to within twice the width of the 114 waveguide. Therefore, among the transverse modes propagating in the 1X1-MMI waveguide regions llla and 111b, a single transverse mode can be reflected with respect to the center wavelength of the grating, thereby achieving a stable single-wavelength operation. Other advantages are the same as those of the first and second embodiments described above.

Next, a method of manufacturing the active MMI semiconductor laser according to the above-described embodiment will be described.

The active MMI semiconductor laser of the present embodiment also basically has a force 1 × 1 MMI waveguide region and grating that can be manufactured by the steps shown in FIGS. 3A to 3F. The region in which the metal is formed is different from the case of the first and second embodiments described above (the steps of FIGS. 3A and 5A). That is, in the present embodiment, as shown in FIG. 7, the grating 120 includes the 1 × 1-MMI waveguide regions ll la and 111b and the sinal mode waveguide region 112 114 on the surface of the n-InP semiconductor substrate 101. In the region where the active waveguide is formed, it is formed over the entire length of the active waveguide. The width of the grating 120 is set to be equal to or larger than the waveguide width of the single mode waveguides 112 to 114 formed in a later step and equal to or smaller than twice the waveguide width. Here, the waveguide width of the single mode waveguide 112 114 is about, and the width of the grating 120 is about 3 μm.

After the formation of the grating 120, an active waveguide including the 1 × 1—MMI waveguide region 11 la, 11 lb and the single mode waveguide region 112 114 is formed. Then, the rear end face and the front end face of the laser element are formed by cleavage, and antireflection films are formed on both end faces, thereby completing the manufacture of the element. Thus, a laser device having the structure shown in FIGS. 6A and 6C is obtained.

[0077] Also in the above manufacturing method, similarly to the manufacturing method in the above-described first embodiment, it is possible to manufacture a low-cost element with a good yield.

The waveguide structure and the method of manufacturing the same according to the present embodiment described above are merely examples, and the configuration and procedure thereof can be changed as appropriate. For example, in the above-described manufacturing process, for example, a molecular beam growth method (MBE method) can be used instead of the MO-VPE method, and an RIE method can be used instead of the ICP method.

Further, the formation position of the grating 120 can be changed within a range where stable single-wavelength oscillation can be obtained. For example, the grating 120 may be provided at any of the positions a) and d) described in the first embodiment. The grating 120 may be provided only in the 1 × 1-M Ml waveguide region l la, 111b. Further, the grating 120 may be provided only on one of the 11_1 ^ 1 ^ 1 waveguide regions 111 & and 11lb.

Further, the number of 1 × 1-MMI waveguide regions can also be changed without increasing the element length. For example, three or more 1 × 1-MMI waveguide regions may be provided.

In the first to third embodiments described above, the active waveguide including the active layer is partially configured by the 1 × 1-M Ml waveguide, but the present invention is not limited to this. What is done For example, it is also possible to use a 1 XN-MMI waveguide or a NXN-MMI waveguide instead of a 1 X 1-MMI waveguide. When a 1 × N-MMI waveguide is used, the “N” side is on the rear side, the “1” side is on the front side, and the single mode waveguide 113 is provided on the rear side at a position corresponding to the N branch. When the NXN-MMI waveguide is used, a single mode waveguide 112 is provided at a position corresponding to the N branch on the front side, and a single mode waveguide 113 is provided at a position corresponding to the N branch on the rear side.

The waveguide structure of each of the above-described embodiments has a structure in which a single mode waveguide is connected to both ends of the MMI waveguide, but only the front or rear side of the MMI waveguide has a single mode. It is also possible to adopt a structure having a mode waveguide. In this case, the end face of the MMI waveguide on which the single mode waveguide is not provided is the laser element end face. For example, when there is no single mode waveguide on the rear side, the rear end face of the MMI waveguide becomes the rear end face of the laser element, and a high reflection film is formed on this end face.

[0083] (Module structure)

Using the active MMI semiconductor laser of the present invention described above, an optical communication module such as an optical transmission module / optical transmission / reception module can be configured. In the case of the optical transmission module, the active MMI semiconductor laser of the present invention and a circuit for driving the semiconductor laser are mounted. In the case of an optical transceiver module, the active MMI semiconductor laser of the present invention, a circuit for driving the semiconductor laser, and a light receiving unit for receiving light input from the outside are mounted. In each case, various other circuits (such as a modulation circuit and a waveform shaping circuit) can be mounted according to the use. These optical communication modules can be driven at a low voltage by using the active MMI semiconductor laser of the present invention. Therefore, it is possible to provide a module which is excellent in low power consumption, which has not existed conventionally.

Claims

The scope of the claims

[1] An active waveguide is composed of at least one multi-mode interference waveguide and at least one single mode waveguide connected to both ends or one end of the multi-mode interference waveguide. A semiconductor laser,

A semiconductor laser having a grating in a part of the active waveguide for selecting a single wavelength of oscillation light propagating through the active waveguide.

2. The semiconductor laser according to claim 1, wherein the grating is provided in a region of the single mode waveguide.

[3] The single mode waveguide is a pair of sinal mode waveguides provided at both ends of the active waveguide,

3. The semiconductor laser according to claim 2, wherein the grating is provided on at least one of the pair of single mode waveguides.

[4] The grating is provided in a region of the multi-mode interference waveguide.

The semiconductor laser according to 1.

[5] The semiconductor laser according to claim 4, wherein the width of the grating is within twice the width of the single mode waveguide.

[6] The single mode waveguide is a pair of sinal mode waveguides provided at both ends of the active waveguide,

6. The semiconductor laser according to claim 5, wherein the grating is provided in an area of the multimode interference waveguide on an extension of the pair of single mode waveguides.

7. The semiconductor laser according to claim 6, wherein said grating is provided over the entire length of said active waveguide.

[8] The semiconductor laser ¹ to ^{1 according} to claim 7, wherein a phase adjustment region is provided in the grating.

[9] An optical communication module that houses the semiconductor laser according to any one of claims 1 to 8 and a circuit that drives the semiconductor laser.

[10] An active waveguide is composed of at least one multimode interference waveguide and at least one single mode waveguide connected to both ends or one end of the multimode interference waveguide. A method of manufacturing a semiconductor laser, comprising:

Forming a grating region having a width larger than the width of the single mode waveguide in a region on the semiconductor substrate where the single mode waveguide is formed;

Etching the grating region into the shape of the active waveguide.

[11] An active waveguide is composed of at least one multimode interference waveguide and at least one single mode waveguide connected to both ends or one end of the multimode interference waveguide. A method for manufacturing a semiconductor laser,

In a region on the semiconductor substrate where the active waveguide is formed, a grating region having a width equal to or larger than the width of the single mode waveguide and within twice the width of the single mode waveguide is placed in the active waveguide. Forming over the entire length of the waveguide;

Etching the grating region into the shape of the active waveguide.