Multi-wavelength laser

Abstract

This provides a multi-wavelength laser that emits multiple wavelengths using a single semiconductor laser. [Solution] The multi-wavelength laser comprises an active layer 103 and a diffraction grating layer having a forward diffraction grating region 161, a backward diffraction grating region 162, and a phase shift region 109 between the forward diffraction grating region and the backward diffraction grating region, wherein the forward diffraction grating region includes one or more grating regions, each of which includes a series of different unit structures, and the backward diffraction grating region has the same structure as the forward diffraction grating region.

Description

[Technical Field]

[0001] This invention relates to multi-wavelength lasers. [Background technology]

[0002] The internet continues to develop as an essential infrastructure of modern society. Optical communication, which excels in high-speed, long-distance communication, accounts for the majority of internet communication, and the continuous increase in internet traffic has made increasing data capacity an urgent issue. To cope with the increase in traffic, technologies such as Wavelength Division Multiplexing (WDM) are being used. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2003-273451 [Overview of the project] [Problems that the invention aims to solve]

[0004] Optical communications that utilize multiple wavelengths, such as WDM communication, require multiple light sources corresponding to the number of wavelengths. For example, if the light source is a semiconductor laser that oscillates at a single wavelength, multiple semiconductor lasers with different oscillation wavelengths are required. On the other hand, tunable lasers, which can vary their oscillation wavelength, are also used. Because tunable lasers can vary their wavelength over a wide range, it is not necessary to prepare semiconductor lasers of different wavelengths. However, a number of tunable lasers corresponding to the number of wavelengths used in WDM communication are required. Also, compared to lasers that oscillate at only one wavelength, tunable lasers have a more complex structure and are less costly in order to set the wavelength.

[0005] The present invention aims to provide a multi-wavelength laser that emits multiple wavelengths using a single semiconductor laser. [Means for solving the problem]

[0006] The multi-wavelength laser comprises an active layer and a diffraction grating layer having a forward diffraction grating region, a backward diffraction grating region, and a phase-shift region between the forward diffraction grating region and the backward diffraction grating region, wherein the forward diffraction grating region includes one or more grating regions, each of which includes a series of different unit structures, and the backward diffraction grating region has the same structure as the forward diffraction grating region. [Brief explanation of the drawing]

[0007] [Figure 1] This is a top view of a multi-wavelength laser according to the first embodiment. [Figure 2] Figure 1 is a schematic cross-sectional view of a multi-wavelength laser along the II-II line. [Figure 3] This is a schematic cross-sectional view of a multi-wavelength laser according to Modification 1 of the First Embodiment. [Figure 4] This is the wavelength spectrum of a multi-wavelength laser according to Modification 1 of the First Embodiment. [Figure 5] This is a schematic cross-sectional view of a multi-wavelength laser according to a modified example 2 of the first embodiment. [Figure 6] This is a top view of a multi-wavelength laser according to a second embodiment. [Figure 7] Figure 6 shows a schematic cross-sectional view along the VII-VII line of a multi-wavelength laser. [Figure 8] This is a top view of a multi-wavelength laser according to the third embodiment. [Figure 9] This is a top view of a multi-wavelength laser according to the fourth embodiment. [Figure 10] Figure 9 shows a schematic cross-sectional view along the XX line of a multi-wavelength laser. [Figure 11] This is a top view of a multi-wavelength laser according to the fifth embodiment. [Figure 12] Figure 11 shows a schematic cross-sectional view along the XII-XII line of a multi-wavelength laser. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described specifically and in detail below with reference to the drawings. Components denoted by the same reference numerals in all figures have the same or equivalent function, and repeated explanations will be omitted. Note that the size of the figures does not necessarily correspond to the magnification.

[0009] [First Embodiment] Figure 1 is a top view of a multi-wavelength laser according to the first embodiment. Figure 2 is a schematic cross-sectional view showing the II-II section of Figure 1.

[0010] The multi-wavelength laser has a semiconductor multilayer on a substrate 101, stacked in the following order: a first conductivity type optical confinement layer 102, an active layer 103, a second conductivity type optical confinement layer 104, a second conductivity type spacer layer 105, a second conductivity type diffraction grating layer 107, and a second conductivity type cladding layer 108. Here, the first conductivity type is n-type and the second conductivity type is p-type, but the order may be reversed. A back electrode 112 is placed on the back surface of the substrate 101, and a front electrode 111 is placed on the side of the second conductivity type cladding layer 108. A contact layer may be placed between the front electrode 111 and the second conductivity type cladding layer 108. Here, the direction in which the active layer 103 and the diffraction grating layer 107 extend is called the first direction D1. The first direction D1 is also called the optical axis direction. A first end face 121 and a second end face 122 are positioned on each side of the first direction D1, and an anti-reflective coating 110 is formed on both the first end face 121 and the second end face 122. The first end face 121 is referred to as the rear end face, and the second end face 122 as the front end face. Here, "front" and "rear" are designations for convenience, and the front and rear can be reversed. The anti-reflective coating 110 is formed to function as an anti-reflective coating in the wavelength range in which this multi-wavelength laser oscillates (all wavelengths from the minimum oscillation wavelength to the maximum oscillation wavelength).

[0011] Here, the substrate 101, the spacer layer 105, and the second conductivity type clad layer 108 are made of InP. The two optical confinement layers 102, 104, the active layer 103, and the diffraction grating layer 107 are composed of InGaAsP, InGaAlAs, etc. These materials are just examples. The active layer 103 is, for example, a multiple quantum well layer with strain applied. The diffraction grating layer 107 has a diffraction grating structure by forming irregularities on the interface with the second conductivity type clad layer 108. Note that irregularities may be formed on the interface between the spacer layer 105 and the diffraction grating layer 107. Here, the semiconductor multilayer is set with a composition wavelength, etc. so as to oscillate in the 1300 nm band, but it is not limited to this and may be other wavelength bands such as the 1550 nm band.

[0012] The cross-section in the direction perpendicular to the optical axis is, for example, a BH structure in which semiconductor layers are arranged on both sides of a mesa structure including the active layer 103, or a ridge structure in which a part of the layer above the active layer 103 (for example, the second conductivity type clad layer 108) has a mesa structure.

[0013] The folded grating layer 107 includes a first diffraction grating region 161, a second diffraction grating region 162, and a phase shift region 109 that generates a λ / 4 phase shift and is disposed between the first diffraction grating region 161 and the second diffraction grating region 162. Here, the first diffraction grating region 161 is disposed between the phase shift region 109 and the rear end face (the first end face 121), and is also referred to as the rear diffraction grating region. The second diffraction grating region 162 is disposed between the phase shift region 109 and the front end face (the second end face 122), and is also referred to as the front diffraction grating region. The front diffraction grating region and the rear diffraction grating region each consist of a grating region 107a. Here, both regions consist of two grating regions 107a. The grating region 107a includes a series of unit structures. The unit structure of the present embodiment is a diffraction grating structure for one period. A plurality of these unit structures gather to form the grating region 107a. In the present embodiment, in the grating region 107a, the period of each unit structure increases from the first unit structure at one end to the second unit structure at the other end. Specifically, the grating region 107a has a first unit structure having the shortest diffraction grating period Λa at the left end on the first end face 121 side, and a second unit structure having the longest diffraction grating period Λb at the right end on the second end face 122 side. The periods of the plurality of unit structures disposed between the first unit structure and the second unit structure increase from the diffraction grating period Λa to the diffraction grating period Λb from the left end on the first end face 121 side toward the right end on the second end face 122 side. In other words, the grating region 107a has a chirped diffraction grating structure. Note that the diffraction grating period Λa and the diffraction grating period Λb may be reversed. That is, in the grating region 107a, the period of each unit structure may decrease from the first unit structure at one end to the second unit structure at the other end. When decreasing the period of each unit structure, the period of each unit structure is decreased from the first unit structure to the second unit structure in the same manner in all grating regions 107a.

[0014] The diffraction grating period Λa and the diffraction grating period Λb have periods corresponding to the minimum wavelength and the maximum wavelength for multi-wavelength oscillation. That is, assuming the effective refractive index of the laser waveguide is n eff the minimum oscillation wavelength λa and the maximum oscillation wavelength λb are

Equation

number

number

[0015] In this example, two lattice regions 107a are arranged in the first diffraction grating region 161 and the second diffraction grating region 162, which sandwich the phase shift region 109. However, the example is not limited to this, and three or more lattice regions 107a may be arranged in the first diffraction grating region 161 and the second diffraction grating region 162 (a total of six lattice regions 107a). When multiple lattice regions 107a are arranged in the first diffraction grating region 161 and / or the second diffraction grating region 162, these multiple lattice regions 107a are adjacent to each other and do not contain any other structures in between.

[0016] [Example 1] Figure 3 is a schematic cross-sectional view along the optical axis of Modification 1 of the multi-wavelength laser according to the first embodiment. The only difference from Figure 2 of the first embodiment is the grating region 107b. When forming the chirp diffraction grating structure shown in the first embodiment, an electron beam lithography apparatus is often used. Some types of apparatus have difficulty forming diffraction gratings with increasing or decreasing periods. In such cases, a grating structure in which the period changes in a stepwise manner, as in this modification, may be used, that is, a grating structure in which each unit structure consists of a series of subunit structures having the same period.

[0017] The lattice region 107b changes in such a way that the diffraction grating period increases sequentially in multiple steps from the minimum diffraction grating period Λ1 to the maximum diffraction grating period Λn. In other words, as shown in Figure 3, the series of unit structures consists of a unit structure consisting of two subunit structures continuous in the first direction D1 at the minimum diffraction grating period Λ1, a unit structure consisting of two subunit structures continuous at a diffraction grating period slightly larger than Λ1, a unit structure consisting of two subunit structures continuous at an even larger diffraction grating period, and finally a unit structure consisting of two subunit structures continuous at the maximum diffraction grating period Λn. In this modified example, for the sake of ease of drawing, the case where each unit structure consists of two subunit structures is illustrated, but each unit structure may consist of three or more subunit structures. That is, each unit structure may be multiple subunit structures. Similar to the first embodiment, four lattice regions 107b are arranged in the direction of the optical axis, and a phase shift region 109 is located between the first diffraction grating region 161 and the second diffraction grating region 162. In this structure as well, a multi-wavelength laser that oscillates simultaneously at multiple wavelengths can be obtained, similar to the first embodiment.

[0018] Figure 4 shows an example of the wavelength spectrum of the multi-wavelength laser according to this modified example. Here, Λ1 = 200.999 nm and Λn = 202.927 nm were set, and the diffraction grating period was changed to increase sequentially in 20 steps within this range. If the wavelength spacing is 1.1285 nm, which corresponds to a 200 GHz spacing, then Ls becomes 232.76 μm. Here, n eff3.22 was used. The diffraction grating layer 107 is composed of four grating regions 107b, so the total resonator length of the multi-wavelength laser is 931 μm. This resonator length also includes the length of the phase-shift region 109. Here, the phase-shift region 109 has a structure in which two concave parts of the concave-concave structure are arranged in succession, and the length of the phase-shift region 109 in the first direction D1 is very short. As shown in Figure 4, with the multi-wavelength laser according to this modified example, oscillation spectra of multiple wavelengths can be obtained. The interval between each wavelength is approximately 1.1 nm. Of these, the eight wavelengths of light located in the center are oscillated simultaneously with almost the same optical output intensity. If the oscillated light containing these eight wavelengths is decoupled using a wavelength decoupler, one semiconductor laser can be used as a light source for eight WDM communications. It is also possible to use it as is without decoupler. For example, if the multi-wavelength light is combined with multiple ring modulators, it is possible to generate individually modulated light for each wavelength without polarization.

[0019] The lattice region 107a in the first embodiment and the lattice region 107b in the modified example 1 are diffraction grating structures that change from a first diffraction grating period to a second diffraction grating period. In the above, the first diffraction grating period corresponds to the minimum wavelength and the second diffraction grating period corresponds to the maximum wavelength, but the reverse is also acceptable. However, even in the reverse case, the lattice structures arranged before and after (at both ends of) the phase shift region 109 are the same. In other words, if the lattice regions 107a and 107b of the first diffraction grating region 161 are a series of unit structures that change from a diffraction grating period corresponding to the maximum wavelength to a diffraction grating period corresponding to the minimum wavelength, then the lattice regions 107a and 107b of the second diffraction grating region 162 are also a series of unit structures that change from a diffraction grating period corresponding to the maximum wavelength to a diffraction grating period corresponding to the minimum wavelength. Furthermore, when multiple grating regions 107a and 107b are arranged in the first diffraction grating region 161 and the second diffraction grating region 162, these multiple grating regions 107a and 107b all consist of a series of unit structures in which the diffraction grating period changes in the same direction.

[0020] [Differentiation 2] Figure 5 is a schematic cross-sectional view along the optical axis of Modification 2 of the multi-wavelength laser according to the first embodiment. The only differences from the first embodiment and Modification 1 are the diffraction grating layer 107 and the grating region 107c. The diffraction grating structure in this modification is a so-called floating type diffraction grating structure, which is arranged in the spacer layer 105 and the second conductive cladding layer 108, rather than having irregularities on the surface of the diffraction grating layer 107. Furthermore, while the first embodiment and Modification 1 show a chirp diffraction grating structure or a stepped chirp diffraction grating structure in which the diffraction grating period changes in a stepped manner, changing the diffraction grating period can increase the writing time and make the writing program enormous depending on the electron beam lithography apparatus. In this embodiment, the diffraction grating period is not changed, and a grating region 107c is provided which has the same effect as the first embodiment and Modification 1 by arranging multiple phase shift sections with different phase shift amounts.

[0021] The stepped chirp diffraction grating structure shown in Modification 1 contains n diffraction grating periods Λs, ranging from the diffraction grating period Λ1 corresponding to the smallest wavelength to the diffraction grating period corresponding to the largest wavelength Λn. If the average value of Λ1 and Λn is denoted by Λstd, then the phase shift amount Φs is

number

[0022] In this modified example of a multi-wavelength laser, one grating region 107c is arranged in the first diffraction grating region 161 and the second diffraction grating region 162, but the invention is not limited to this, and multiple grating regions 107c may be arranged as shown in the first embodiment.

[0023] [Second Embodiment] Figure 6 is a top view of a multi-wavelength laser according to the second embodiment. Figure 7 is a schematic cross-sectional view showing the VII-VII section of Figure 6.

[0024] The multi-wavelength laser according to this embodiment includes a passive waveguide section 203, a DFB section 201, and an optical amplifier (SOA: semiconductor optical amplifier) ​​section 202, extending from the first end face 121 to the second end face 122 in the first direction D1. The DFB section 201 has the same structure as the multi-wavelength laser described in Modification 2 of the first embodiment. These three regions also have a waveguide (mesa structure) 250. The shape of the waveguide 250 when viewed from above cannot be seen in plan view because it is located beneath electrodes and other components, which will be described later. Therefore, its shape is shown by a dotted line in Figure 6.

[0025] The passive waveguide section 203 includes, in this order, a passive waveguide lower optical confinement layer 114, a passive waveguide core layer 113, and a passive waveguide upper optical confinement layer 115 on the substrate 101. A second conductive cladding layer 108 is arranged on top of the passive waveguide upper optical confinement layer 115. The passive waveguide section 203 does not include a diffraction grating layer 107. The passive waveguide core layer 113 is composed of a semiconductor layer such as a bulk or multiple quantum well layer that does not absorb the light oscillated in the DFB section 201.

[0026] The semiconductor multilayer included in the SOA section 202 has the same structure as the DFB section 201, except that the diffraction grating layer 107 is not present. However, the semiconductor multilayer included in the SOA section 202 may have a different structure from that of the DFB section 201. The SOA section 202 is equipped with an SOA section surface electrode 116 on the second conductive cladding 108. The SOA section surface electrode 116 may be formed integrally with the surface electrode 111 of the DFB section 201. The output light of the DFB section 201 can be increased by injecting current into the SOA section surface electrode 116. However, it is desirable to keep the optical amplification of the SOA section 202 at a level that does not significantly affect the adverse effects of four-wave mixing.

[0027] The wavelength spacing of a multi-wavelength laser is determined by equation (3), so the resonator length as a laser is important. In this configuration, the diffraction grating layer 107 does not reach the first end face 121 and the second end face 122, so the region in which the diffraction grating layer 107 is formed is determined by the drawing region of the diffraction grating structure. The positional accuracy of the drawing region of the diffraction grating structure is sufficiently high, and the resonator length can be formed to the designed length. For example, in the case of the multi-wavelength laser shown in the first embodiment, the positions of the first end face 121 and the second end face 122 and the positions of both ends of the diffraction grating layer are approximately coincident. This is because multiple multi-wavelength lasers are formed on the wafer and then chipped by cleavage or the like. In this chipping process, if the cleavage position is shifted in the first direction D1, the length of the grating region 107a in contact with the first end face 121 and the length of the grating region 107a in contact with the second end face 122 may be different. As a result, there is a risk that the desired multi-wavelength oscillation cannot be achieved.

[0028] Furthermore, a window structure may be placed between the DFB section 201 and at least one of the first end face 121 and the second end face 122. Even if the lengths of the window structures on the first end face 121 side and the second end face 122 side change during the chipping process, the length of the diffraction grating layer 107 remains unchanged, thus enabling stable multi-wavelength oscillation.

[0029] [Third Embodiment] Figure 8 is a top view of a multi-wavelength laser according to the third embodiment. The multi-wavelength laser according to this embodiment includes a passive waveguide section 303, a DFB section 301, and an optical amplification section 302, similar to the second embodiment. Each semiconductor multilayer is the same as in the second embodiment. The difference from the second embodiment is the shape of the waveguide 350 through which the light propagates.

[0030] In this embodiment, the waveguide 350 is a straight line along the first direction D1 in the DFB section 301, but includes curved sections in the SOA section 302 and the passive waveguide section 303. This configuration makes it possible to suppress the reflection of light from the first end face 121 and the second end face 122. Since an anti-reflective coating is formed on the first end face 121 and the second end face 122, the reflection of light at each end face is sufficiently small. However, it is difficult to completely eliminate reflection. Furthermore, the reflected light from the second end face 122 may be amplified in the SOA section 302. If light reflection from the end faces is added in addition to the reflection of light from the diffraction grating structure, there is a risk of oscillation at unintended wavelengths or affecting the light output intensity at each wavelength. In this embodiment, the waveguide 350 between the diffraction grating layer 107 and each end face is curved, which makes it possible to suppress the effect of reflection at each end face and obtain multi-wavelength oscillation as designed.

[0031] [Fourth Embodiment] Figure 9 is a top view of a multi-wavelength laser according to the fourth embodiment. Figure 10 is a schematic cross-sectional view showing the XX cross-section of Figure 9.

[0032] In this embodiment, the multi-wavelength laser has a DBR section 403 and a DFB section 401 arranged side by side in the first direction D1, from the first end face 121 to the second end face 122. The DFB section 401 has the same structure as the multi-wavelength laser described in Modification 2 of the first embodiment.

[0033] The DBR section 403 includes, in this order, a DBR lower optical confinement layer 414, a DBR core layer 413, and a DBR upper optical confinement layer 415 on the substrate 101. A second conductive cladding layer 108 is placed on top of the DBR upper optical confinement layer 415. The DBR section 403 also includes a diffraction grating layer 107. The diffraction grating layer 107 included in the DBR section 403 includes two grating regions 107c. Furthermore, there is no λ / 4 phase shift region between the two grating structures 107c.

[0034] The operation of the multi-wavelength laser according to this embodiment will now be described. The DFB unit 401 oscillates in multiple wavelengths when current is injected, as in other embodiments. In the first embodiment, an anti-reflective film 110 is formed on both the first end face 121 and the second end face 122. The same structure (the same number of lattice regions 107a, 107b, and 107c) is arranged on either side of the phase shift region 109. Therefore, the optical output intensity output from the first end face 121 and the optical output intensity output from the second end face 122 are theoretically the same. In semiconductor lasers used for optical communication, it is common to use only the light output from one end face, and it is desirable for the optical output intensity from one end face to be high. The multi-wavelength laser according to this embodiment can achieve a higher optical output intensity from the second end face 122 compared to the multi-wavelength laser according to Modification 2 of the first embodiment. In this embodiment, the optical output intensity output from the first end face 121 is lower. The DBR section 403 is a passive region to which no current is injected, but because a lattice region 107c is present, it reflects light towards the DFB section 401. In this embodiment, since the DBR section 403 has the same lattice region 107c as the DFB 401, it can reflect multi-wavelength light emitted by the DFB section 401. In other words, by reflecting the light that would have originally been output from the first end face 121 towards the second end face 122, the light output intensity output from the second end face 122 can be increased. Note that the number of lattice regions 107c included in the DBR section 403 is not limited to two; it can be one or three or more.

[0035] [Fifth Embodiment] Figure 11 is a top view of a multi-wavelength laser according to the fifth embodiment. Figure 12 is a schematic cross-sectional view showing the XII-XII section of Figure 11. The multi-wavelength laser according to this embodiment has the same semiconductor multilayer as the multi-wavelength laser according to the first embodiment, except for the structure of the diffraction grating layer 507.

[0036] The multi-wavelength laser includes a first diffraction grating region 561, a phase-shift region 509, and a second diffraction grating region 562 in the first direction D1, extending from the first end face 121 to the second end face 122. Each region has the same semiconductor multilayer except for the structure of the diffraction grating layer.

[0037] In the first diffraction grating region 561, the diffraction grating layer has a multi-stage structure. Here, the multi-stage structure includes a first diffraction grating layer 507 and a second diffraction grating layer 557 positioned above the first diffraction grating layer 507. The region sandwiched between the first diffraction grating layer 507 and the second diffraction grating layer 557 is made of the same material as the second conductive cladding layer 108. The positions of each unit structure in the second diffraction grating layer are aligned with the positions of each unit structure in the first diffraction grating layer. That is, the diffraction grating period of the first diffraction grating layer 507 and the diffraction grating period of the second diffraction grating layer 557 are the same. Furthermore, the arrangement of the grating regions 107d is in the same phase as the grating region 107c in the modified example 2 of the first embodiment. In other words, uniform diffraction grating regions and phase-shifted regions are arranged alternately. The first diffraction grating region 561 includes two grating regions 107d.

[0038] In the second diffraction grating region 562, three grating regions 107c are arranged, similar to those in Modification 2 of the first embodiment. In other words, only the first diffraction grating layer 507 is arranged in the second diffraction grating region 562, and the second diffraction grating layer 557 is not arranged. In the region of the second diffraction grating region 562 that is at the same height from the substrate as the second diffraction grating layer 557 arranged in the first diffraction grating region 561, the second conductive cladding layer 108 is arranged. The grating regions 107c of the second diffraction grating region 562 and the grating regions 107d of the first diffraction grating region 561 differ in the number of diffraction grating layers, but the phase of the diffraction grating structure is the same. That is, the grating regions 107c and grating regions 107d have the same series of unit structures.

[0039] The length of the phase shift region 509 in the first direction D1 is greater than the length of the phase shift region 109 in the first direction D1 in the λ / 4 phase shift structure of the first embodiment. In the first embodiment, an example was shown in which the phase shift region 109 shifts the phase of the diffraction grating by π, but in this embodiment and others, the phase shift amount of the phase shift region 109 can be (2n+1)π (where n is an integer greater than or equal to 0). In this embodiment, the length of the phase shift region 509 is set to be larger in order to connect the first diffraction grating region 561 and the second diffraction grating region 562, which have different widths of mesa structures (details will be described later).

[0040] In this embodiment, since the number of diffraction grating layers in the first diffraction grating region 561 is greater than the number of diffraction grating layers in the second diffraction grating region 562, the coupling coefficient κ of light is high in the first diffraction grating region 561. Therefore, according to this embodiment, the amount of light emitted from the second end face 122 is greater than the amount of light emitted from the first end face 121. Also, as in other embodiments, multi-wavelength oscillation is realized because the same phase grating structure (the same series of unit structures) is provided before and after the phase shift region 509. Furthermore, although the number of grating regions included in the first diffraction grating region 561 is different from the number of grating regions included in the second diffraction grating region 562, multi-wavelength oscillation is realized as long as at least one grating region is included in both the first diffraction grating region 561 and the second diffraction grating region 562. Note that the number of diffraction grating layers is not limited to two stages.

[0041] In this embodiment, the multi-wavelength laser has different mesa widths in the first diffraction grating region 561 and the second diffraction grating region 562. As shown in Figure 11, the mesa width of the first diffraction grating region 561 is narrower than that of the second diffraction grating region 562. The mesa width changes smoothly in the phase shift region 509. This structure allows the effective refractive index n of the first diffraction grating region 561 to be eff and the effective refractive index n of the second diffraction grating region 562 eff This combines the two. In other words, because the first diffraction grating region 561 has multiple diffraction grating layers, the effective refractive index n of the first diffraction grating region 561 effis higher than the effective refractive index n of the second diffraction grating region 562 eff Therefore, when the mesa width and the drive current are the same throughout, the wavelengths reflected by the grating structure may deviate between the first diffraction grating region 561 and the second diffraction grating region 562, which may result in disturbing stable multi-wavelength oscillation. To avoid this, the mesa width is used to adjust the effective refractive index n of the first diffraction grating region 561 eff and the effective refractive index n of the second diffraction grating region 562 eff to be the same.

[0042] The present invention is not limited to the above-described embodiments, and various modifications are possible. The configurations described in the embodiments can be replaced with configurations having substantially the same configuration, the same operational effects, or configurations capable of achieving the same object. For example, the diffraction grating layer may be disposed between the substrate and the active layer. Also, the grating structures after the second embodiment may be replaced with the grating region 107a of the first embodiment or the grating region 107b of the modification example 1.

[0043] The present invention relates to a multi-wavelength laser that oscillates simultaneously at multiple wavelengths in a DFB laser. The multi-wavelength laser includes an active layer and a diffraction grating layer, with anti-reflective coatings formed on both end faces. The diffraction grating layer achieves multi-wavelength oscillation by providing a λ / 4 phase-shift region and grating regions containing a series of unit structures before and after the λ / 4 phase-shift region in the optical axis direction. The series of unit structures have a diffraction grating period that changes gradually or stepwise from a first diffraction grating period to a second diffraction grating period. Alternatively, in the series of unit structures, uniform diffraction grating structures and phase-shift sections are arranged alternately, and the phase shift amount of each phase-shift section is different from that of the others. Multiple grating regions may be arranged between the front end face and the phase-shift region and / or between the rear end face and the phase-shift region. When multiple grating regions are arranged, the grating regions are adjacent to each other. The multi-wavelength laser may include a DFB laser section that performs multi-wavelength oscillation, a passive waveguide section arranged between the DFB laser section and the rear end face, and an optical amplification section arranged between the DFB laser section and the front end face. A multi-wavelength laser has a mesa structure through which light propagates in a plan view, and in the passive waveguide section and the optical amplification section, the mesa structure may be curved with respect to the optical axis. Furthermore, a multi-wavelength laser may include a DFB laser section that oscillates at multiple wavelengths, and a DBR section between the DFB laser section and the rear end face. The DBR section has the same grating region as the grating region included in the DFB laser section. When the multi-wavelength laser has a first diffraction grating region between the λ / 4 phase shift region and the rear end face, and a second diffraction grating region between the λ / 4 phase shift region and the front end face, the number of stages of the diffraction grating layers included in the first diffraction grating region and the number of stages of the diffraction grating layers included in the second diffraction grating region may be different. For example, the first diffraction grating region may include two stages of diffraction grating layers, and the second diffraction grating region may include one stage of diffraction grating layers. Between the two stages of diffraction grating layers, the phase of the series of unit structures is the same, and the grating regions of the first diffraction grating region and the grating regions of the second diffraction grating region are arranged in the same way except for the number of stages of the diffraction grating layers. Structures that include a DBR (Deep Burner) section, or those with a different number of diffraction grating layers, increase the light output intensity emitted from the front. The oscillation wavelength band of the multi-wavelength laser can be the 1.3 μm band, the 1.55 μm band, or any other wavelength band. [Explanation of Symbols]

[0044] 101 Substrate 102 First conductivity type optical confinement layer 103 Active layer 104 Second conductivity type optical confinement layer 105 Spacer layer 107 Diffraction grating layers 107a, 107b, 107c, 107d Grating region 108 Second conductivity type cladding layer 109, 509 Phase shift region 110 Anti-reflective film 111 Surface electrode 113 Waveguide core layer 114 Passive waveguide lower optical confinement layer 115 Passive waveguide upper optical confinement layer 116 SOA section surface electrode 121 First end face 122 Second end face 147 Uniform grating structure 161, 561 First diffraction grating region 162, 562 Second diffraction grating region 201, 301, 401 DFB section 202, 302 Optical amplification section 203, 303 Passive waveguide section 250, 350 Mesa structure 404 DBR section 413 DBR core layer 414 DBR lower light confinement layer 415 DBR upper light confinement layer 507 First diffraction grating layer 557 Second diffraction grating layer D1 First direction

Claims

1. The active layer, A diffraction grating layer comprising a forward diffraction grating region, a backward diffraction grating region, and a phase-shift region between the forward diffraction grating region and the backward diffraction grating region, The forward diffraction grating region includes one or more grating regions, Each of the one or more lattice regions includes a series of unit structures that are different from each other. A multi-wavelength laser in which the back diffraction grating region has the same structure as the front diffraction grating region.

2. A multi-wavelength laser according to claim 1, The aforementioned phase-shift region is a multi-wavelength laser with a λ / 4 phase-shift structure.

3. A multi-wavelength laser according to claim 1, A multi-wavelength laser in which, in each of the aforementioned lattice regions, the period of each unit structure increases or decreases as you move from the first unit structure at one end to the second unit structure at the other end.

4. A multi-wavelength laser according to claim 1, Each of the aforementioned unit structures comprises a series of subunit structures having the same period, in a multi-wavelength laser.

5. A multi-wavelength laser according to claim 1, In each of the aforementioned grating regions, the uniform diffraction grating structure and the phase-shifted portion included in the series of unit structures are arranged alternately. A multi-wavelength laser wherein the phase shift amounts of the phase shift portions included in each of the aforementioned unit structures are different from each other.

6. A multi-wavelength laser according to claim 1, A multi-wavelength laser having a first end face and a second end face on each side in the first direction in which the active layer and the diffraction grating layer are stretched.

7. A multi-wavelength laser according to claim 1, A multi-wavelength laser in which the one or more lattice regions are arranged adjacent to each other.

8. A multi-wavelength laser according to claim 6, A multi-wavelength laser further comprising: an optical amplification unit disposed between the forward diffraction grating region and the second end face; and a passive waveguide unit disposed between the backward diffraction grating region and the first end face.

9. A multi-wavelength laser according to claim 8, Equipped with a waveguide through which light propagates, A multi-wavelength laser in which, in a plan view, the waveguide is bent with respect to the first direction at the passive waveguide section and the optical amplification section.

10. A multi-wavelength laser according to claim 6, A multi-wavelength laser further comprising a DBR portion disposed between the rear diffraction grating region and the first end face, and including the diffraction grating layer.

11. A multi-wavelength laser according to claim 1, In the aforementioned back diffraction grating region, the diffraction grating layer has a multi-stage structure including a first diffraction grating layer and a second diffraction grating layer. The positions of each unit structure in the second diffraction grating layer are aligned with the positions of each unit structure in the first diffraction grating layer. Multi-wavelength laser.

12. A multi-wavelength laser according to claim 11, Equipped with a waveguide through which light propagates, A multi-wavelength laser in which, in a plan view, the width of the waveguide in the forward diffraction grating region is wider than the width of the waveguide in the backward diffraction grating region in a second direction perpendicular to the first direction in which the active layer and the diffraction grating layer extend.

13. A multi-wavelength laser according to claim 1, A multi-wavelength laser further comprising an electrode spanning the forward diffraction grating region, the backward diffraction grating region, and the phase shift region.

14. A multi-wavelength laser according to claim 6, A multi-wavelength laser in which an anti-reflective coating is formed on the first end face and the second end face, respectively.

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