JP5713378B2 - Waveguide type optical filter and semiconductor laser - Google Patents

Description

  The present invention relates to a waveguide-type optical filter including a multimode interference waveguide and a semiconductor laser.

  In recent years, with the progress of the information and communication society by the Internet, not only the backbone network but also the wavelength division multiplexing technology (WDM: Wavelength) has been applied to the local area network to cope with future information demand and new services. Division Multiplex)) has been applied. However, in local area networks, wavelength multiplexing (CWDM) that uses a wide wavelength range, not wavelength multiplexing (DWDM (Dense WDM)), which is popular in backbone networks, especially from the viewpoint of cost and network management operation (Coarse WDM) method is generally used.

  One of the key devices for realizing the wavelength multiplexing system is a wavelength filter that can select a desired wavelength. In the DWDM system, AWG (Arrayed Waveguide Grating) is widely used. (For example, refer to Patent Document 1).

  Also, in the CWDM system, a filter that covers a wide wavelength range is necessary, so AWG is not appropriate, and until now, realistic measures such as inserting a multilayer filter plate have been taken. However, in this method, basic wavelength filtering in which one of the two wavelengths is selected may be used. However, as the number of wavelengths increases, the number of insertion points of the multilayer filter plate increases, which is mechanical insertion. However, there is a limit because the optical loss due to this cannot be ignored. Therefore, there is an urgent need to develop a waveguide type optical filter that can be easily integrated with a semiconductor laser or a semiconductor light receiving element.

  On the other hand, Mach-Zehnder type and ladder type optical filters have been reported as waveguide type optical filters that have a relatively high degree of design freedom and can be used for CWDM filter design (for example, Non-Patent Document 1 and Non-Patent Document 2).

  By the way, with respect to the light source in the local area network, with the progress of the information communication society by the Internet, the existing light source has a technical limit, and an attempt to increase the amount of information has been studied. In addition, since it is necessary to reduce the cost as much as possible, it is necessary to avoid the use of an optical modulator, which is common in a backbone network, as much as possible, and to study the high speed based on direct modulation of a semiconductor laser.

  On the other hand, as a structure in which a part of the cavity is a direct modulation region and the relaxation oscillation frequency can be increased, a distributed reflection (DR) and distributed flag reflection (DBR) type semiconductor laser is used. Have been reported (for example, see Non-Patent Document 3 and Non-Patent Document 4).

  In addition, the conventional semiconductor laser includes a 1 × 3 type multimode interference waveguide, one optical waveguide that guides light provided at one end of the multimode interference waveguide, and a multimode interference waveguide. And three optical waveguides (straight waveguide and curved waveguide) for guiding laser light. A part of one straight waveguide and two curved waveguides constitutes an optical phase matching region so that the phase of light is matched at each front end face, and a resonator is provided between the rear end face and the front end face. (For example, refer patent document 2).

Japanese Patent Laid-Open No. 11-72633 JP 2009-54699 A Yasuhiro Hida et al., "Wavelength multiplexer / demultiplexer with non-sinusoidal filter characteristics constructed by point-symmetric connection of Mach-Zehnder interferometer", IEICE Transactions CI, Vol. J80-CI, No. 11, The Institute of Electronics, Information and Communication Engineers, November 1997, pp. 517-524 The Institute of Electronics, Information and Communication Engineers Matsuo Shinji et al., “Wavelength Tunable Laser Using Ladder Type Filter and Ring Resonator”, IEICE Technical Report LQE, 103 (526), The Institute of Electronics, Information and Communication Engineers, December 2003, pp. 33-36 T. Kakitsuka et al., "20-km Transmission of 40-Gb / s Signal using Frequency Modulated DBR Laser", Optical Fiber Communication Conference 2009, OThG4 K. Otsubo et al., `` Low-Driving-Current High-Speed Direct Modulation up to 40 Gb / s Using 1.3-μm Semi-Insulating Buried-Heterostructure AlGaInAs-MQW Distributed Reflector (DR) Lasers '', Optical Fiber Communication Conference 2009, OThT6

  The conventional optical waveguide type filter is an arrayed waveguide type filter, and the distance between the arrayed waveguides is centered so that the propagation light is imaged by the output side slab waveguide and guided to the output waveguide. Regularity that satisfies an integral multiple of the wavelength is required. In addition, the conventional optical waveguide filter needs to have a basic structure that is exactly symmetrical with respect to the center line of the arrayed waveguide, and must form two slab waveguides according to the Roland circle configuration. There is a problem that there are manufacturing restrictions.

  Also, conventional Mach-Zehnder type and ladder type optical filters basically divide incident light into two and then combine them after passing through different waveguide lengths. Corresponding to the phase difference, it is based on the principle that what is out of phase is emitted and what is in phase is transmitted. However, in order to obtain a desired transmission characteristic, it is necessary to perform several stages of superposition in the waveguide direction. As a result, there is a problem that the total length of the optical filter is increased. In addition, the conventional Mach-Zehnder type and ladder type optical filters have a structure that becomes complicated due to several stages of superposition in the waveguide direction, leading to a decrease in yield, and in turn a cost. There is.

Furthermore, both of the conventional distributed reflection and distributed flag reflection type semiconductor lasers have a structure in which a grating for emitting light at a single wavelength is included in the entire waveguide or a part thereof. There exists a subject that manufacturing cost becomes comparatively high. In particular, the conventional distributed reflection and distributed flag reflection type laser has a problem that it is difficult to apply to a local area network or the like where cost reduction is severe.
Further, the conventional semiconductor laser only discloses means for matching the phase of light at the front end face, and does not provide means for reaching single-wavelength oscillation.

  The present invention has been made to solve the above-described problems, and provides a waveguide-type optical filter that can be reduced in size and cost as compared with a conventional waveguide-type optical filter. Is. The present invention also provides a semiconductor laser capable of realizing a low-cost light source as compared with a conventional semiconductor laser.

In the waveguide type optical filter according to the present invention, the input of a 1 × N type multimode interference waveguide having one input and N (N is an integer of 3 or more) output and the input of a 1 × N type multimode interference waveguide One end is connected to each port on the output side of the first optical waveguide group consisting of one optical waveguide whose one end is connected to the port on the side and the 1 × N type multimode interference waveguide , and three or more types are different a second optical waveguide group consisting of N optical waveguides that have a waveguide length, provided with, the other end of the optical waveguide of the first optical waveguide group and an entrance surface and the exit surface, the second optical waveguide The other end of each optical waveguide of the group is a reflecting surface, and the waveguide length of one optical waveguide of the second optical waveguide group is a plurality of other optical waveguides having two or more different waveguide lengths . Unlike waveguide length, for waveguide length of one optical waveguide of the second optical waveguide group, the second light Based on differences between the waveguide length of the plurality of other waveguides of waveguide group, the wavelength peak period Δλ is the distance of the repetition peak of the transmitted light from the exit surface, a plurality of present and satisfy the following formula 1 each When the integer is m and the difference between the waveguide length of one optical waveguide of the second optical waveguide group and each waveguide length of a plurality of other optical waveguides of the second optical waveguide group is Δd / 2. The following formula 2 is satisfied.
[Formula 1]
m = λ ₀ / Δλ
(Where λ _{0 is the} incident light wavelength, Δλ is the wavelength peak period)
[Formula 2]
Δd = λ ₀ (Φ ₀ + 2π (m−1)) / 2πn _eq
(Where n _{eq is} the equivalent refractive index of the optical waveguide of the second optical waveguide group, Φ _{0 is the} initial matching phase)

In the semiconductor laser according to the present invention, a 1 × N type multimode interference waveguide of 1 input and N (N is an integer of 3 or more) output type, and a port on the input side of the 1 × N type multimode interference waveguide One end is connected to each of the ports on the output side of the 1 × N type multimode interference waveguide, and one or more different waveguide lengths are formed. A second optical waveguide group consisting of N optical waveguides having the other end of each optical waveguide of the second optical waveguide group, the other end of the optical waveguide of the first optical waveguide group being the exit surface 1 × N-type multimode interference waveguide, the first optical waveguide group, and the second optical waveguide group have a layer structure having an active layer, and one of the second optical waveguide groups A plurality of other light beams having two or more different waveguide lengths. Unlike the waveguide length of the waveguide, based on the difference between the waveguide lengths of a plurality of other waveguides of the second optical waveguide group with respect to the waveguide length of one optical waveguide of the second optical waveguide group, There are a plurality of wavelength peak periods Δλ, which are intervals between repeated peaks of transmitted light from the emission surface, and each integer satisfying the following formula 5 is set to m, with respect to the waveguide length of one optical waveguide of the second optical waveguide group. When the difference from each waveguide length of a plurality of other optical waveguides of the second optical waveguide group is Δd / 2, the following Expression 6 is satisfied.
[Formula 5]
m = λ ₀ / Δλ
(Where λ _{0 is the} incident light wavelength, Δλ is the wavelength peak period)
[Formula 6]
Δd = λ ₀ (Φ ₀ + 2π (m−1)) / 2πn _eq

  In the waveguide type optical filter according to the present invention, it is possible to superimpose a plurality of different optical filter characteristics within the same element length, and it is possible to reduce the size and cost as compared with the conventional waveguide type optical filter. Can be planned.

  In the semiconductor laser according to the present invention, a single-wavelength light source that does not require a grating can be realized, and a low-cost light source can be realized as compared with a conventional semiconductor laser. Furthermore, in the semiconductor laser according to the present invention, since the multimode interference waveguide has a wider waveguide width than each optical waveguide of the first optical waveguide group and the second optical waveguide, a high current can be obtained. It can be injected and high output can be easily realized.

(A) is a top view which shows an example of schematic structure of the waveguide type optical filter which concerns on 1st Embodiment, (b) is another schematic structure of the waveguide type optical filter which concerns on 1st Embodiment It is a top view which shows an example. 2A is a cross-sectional view taken along line AA ′ of the waveguide type optical filter shown in FIG. 1, and FIG. 2B is a cross section taken along line BB ′ of the waveguide type optical filter shown in FIG. FIG. It is explanatory drawing explaining the principle of the waveguide type optical filter which concerns on 1st Embodiment, (a) is a transmission spectrum in case a transmission peak appears about every 26 nm, (b) is transmitted every about 13 nm. It is a transmission spectrum when a peak appears. It is explanatory drawing explaining the principle of the waveguide type optical filter which concerns on 1st Embodiment, (a) is a transmission spectrum in case a transmission peak appears for every about 26 nm, and transmission in case a transmission peak appears for about every 13 nm. It is the figure which superimposed the spectrum, (b) is the transmission spectrum obtained by the waveguide type optical filter shown in FIG. It is explanatory drawing explaining the manufacturing method of the waveguide type optical filter which concerns on 1st Embodiment, (a) respond | corresponds to sectional drawing of the arrow AA 'line of the waveguide type optical filter shown in FIG. is a cross-sectional view of a state in which a SiO ₂ film is deposited on the SOI substrate, (b) is a state of forming a mask corresponding to the cross-sectional view of the arrow line a-a 'of the waveguide type optical filter shown in FIG. 1 It is sectional drawing. It is a figure explaining the manufacturing method of the waveguide type optical filter which concerns on 1st Embodiment, (a) is the etching corresponding to sectional drawing of the arrow AA 'line of the waveguide type optical filter shown in FIG. FIG. 2B is a cross-sectional view of the waveguide type optical filter shown in FIG. 1 with the mask removed corresponding to the cross-sectional view taken along the line AA ′ of FIG. . (A) is a top view which shows an example of schematic structure of the waveguide type optical filter in case the number of the optical waveguides of the 2nd optical waveguide group shown to Fig.1 (a) is three, (b) is FIG. It is a top view which shows an example of schematic structure of the waveguide type optical filter in case the optical waveguide of the 2nd optical waveguide group shown to a) is four, (c) is the 2nd shown in Fig.1 (a). It is a top view which shows an example of schematic structure of a waveguide type optical filter in case the number of the optical waveguides of an optical waveguide group is five. It is the transmission spectrum figure by each waveguide type optical filter shown in FIG. (A) is a top view which shows an example of schematic structure of a waveguide type optical filter in case the number of the optical waveguides of the 2nd optical waveguide group shown to Fig.1 (a) is nine, (b) is FIG. It is the transmission spectrum figure by the waveguide type optical filter shown to a), (c) is explanatory drawing which shows the relationship between the number of the optical waveguides of the 2nd optical waveguide group shown to Fig.1 (a), and SMSR. (A) is a top view which shows an example of schematic structure of the waveguide type optical filter which concerns on 2nd Embodiment, (b) is arrow CC of the waveguide type optical filter shown to Fig.10 (a). It is sectional drawing of a line. (A) is a top view which shows an example of schematic structure of the semiconductor laser which concerns on 3rd Embodiment, (b) is a top view which shows the other example of schematic structure of the semiconductor laser which concerns on 3rd Embodiment. is there. (A) is sectional drawing of the arrow D-D 'line of the semiconductor laser shown in FIG. 11, (b) is sectional drawing of the arrow E-E' line of the semiconductor laser shown in FIG. It is explanatory drawing explaining the manufacturing method of the semiconductor laser which concerns on 3rd Embodiment, (a) is a crystal structure by the MOVPE method corresponding to sectional drawing of the arrow DD 'line of the semiconductor laser shown in FIG. It is sectional drawing of the manufactured state, (b) is sectional drawing of the state in which the mask corresponding to sectional drawing of the arrow DD- 'line of the semiconductor laser shown in FIG. 11 was formed. It is explanatory drawing explaining the manufacturing method of the semiconductor laser which concerns on 3rd Embodiment, (a) forms a high mesa structure by the etching corresponding to sectional drawing of the arrow DD 'line of the semiconductor laser shown in FIG. It is sectional drawing of the state which carried out, (b) is sectional drawing of the state embedded with BCB corresponding to sectional drawing of the arrow DD- 'line of the semiconductor laser shown in FIG. (A) is a top view which shows an example of schematic structure of the semiconductor laser which concerns on 4th Embodiment, (b) is sectional drawing of the arrow FF 'line of the semiconductor laser shown to Fig.15 (a). is there.

(First embodiment of the present invention)
The waveguide type optical filter 100 is provided with an optical waveguide and a multimode interference waveguide on the substrate 10, branches light incident from outside, matches the phase of the light, and combines the light. And exits to the outside. For this reason, the waveguide type optical filter 100 uses the end face of the optical waveguide on the one end face 10a side of the substrate 10 as the incident face, and the end face of the optical waveguide on the other end face 10b side facing the one end face 10a of the substrate 10 as the exit face. In this case, it is necessary to provide multimode interference waveguides for demultiplexing and multiplexing, respectively. In this case, the waveguide type optical filter 100 includes a first optical waveguide group 1, a second optical waveguide group 2, a third optical waveguide group 3, and an M × N type multimode interference waveguide 4 described later. And at least the N × M ′ type multimode interference waveguide 5 (see, for example, FIG. 1A).

  Further, the waveguide type optical filter 100 has an end face of the optical waveguide on the one end face 10a side of the substrate 10 as an incident face and an exit face, and an end face of the optical waveguide on the other end face 10b side of the substrate 10 as a reflecting face. What is necessary is just to provide the multimode interference waveguide which uses both demultiplexing and multiplexing. In this case, the waveguide type optical filter 100 includes at least the first optical waveguide group 1, the second optical waveguide group 2, and the M × N type multimode interference waveguide 4 (for example, FIG. 1B). reference).

  In the present embodiment, the case where the end face of the optical waveguide on the one end face 10a side of the substrate 10 is an incident face and the end face of the optical waveguide on the other end face 10b side of the substrate 10 is an outgoing face will be described as an example. However, the waveguide-type optical filter 100 may be configured such that the end face of the optical waveguide on the one end face 10a side of the substrate 10 is the entrance face and the exit face, and the end face of the optical waveguide on the other end face 10b side of the substrate 10 is the reflection face. .

  As shown in FIG. 1A, a waveguide type optical filter 100 according to the present embodiment includes a first optical waveguide group 1 as an incident optical waveguide and an M × N type multimode interference guide on a substrate 10. The waveguide 4, the second optical waveguide group 2 as the optical phase matching region 20, the N × M ′ type multimode interference waveguide 5, and the third optical waveguide group 3 as the output optical waveguide are integrated. Yes.

  The M × N type multi-mode interference waveguide 4 is a multi-mode interference waveguide of M (M is an integer of 1 or more) input and N (N is an integer of 3 or more) output type. In the present embodiment, the 1 × 3 type multimode interference waveguide 4a in which M is 1 and N is 3 will be described as an example. However, the present embodiment is limited to this 1 × 3 type multimode interference waveguide 4a. It is not something that can be done. In particular, the 1 × 3 type multimode interference waveguide 4a according to the present embodiment has a waveguide length along the light guiding direction (hereinafter referred to as the waveguide length) of about 280 μm, and the waveguide width. Has a substantially rectangular interference region of about 20 μm.

  The N × M′-type multimode interference waveguide 5 is a multimode interference waveguide that has N (N is an integer of 3 or more) input and M ′ (M ′ is an integer of 1 or more) output type. In the present embodiment, a 3 × 1 type multimode interference waveguide 5a in which N is 3 and M ′ is 1 will be described as an example, but the 3 × 1 type multimode interference waveguide 5a is described as an example. It is not limited. In particular, the 3 × 1 type multimode interference waveguide 5a according to this embodiment has a substantially rectangular interference region having a waveguide length of about 280 μm and a waveguide width of about 20 μm.

  The multimode interference waveguide can be designed using a known technique. For example, based on the MMI (Multimode Interference) theory, the M × N type multimode interference waveguide 4 and the N × N The M ′ type multimode interference waveguide 5 can be designed as follows.

The expression of the length (Lπ) of the multimode interference waveguide can be expressed as the following formula 1. Where W ₁ represents the width of the multimode interference region, Nr represents the refractive index of the waveguide, Nc represents the refractive index of the cladding, and λ ₀ represents the incident light wavelength. Also, σ represents σ = 0 in the TE mode, and σ = 1 in the TM mode.

[Equation 1]
W _e = W ₁ + (λ ₀ / π) (Nc / Nr) ² σ (Nr ² −Nc ² ) ^−1/2 (1)
Lπ = 4NrW _e ² / 3λ ₀
Further, the multimode interference waveguide can operate as a 1 × N type optical waveguide when expressed by the following equation (2). The multi-mode interference waveguide can operate as an M × N type optical waveguide when expressed by the following equation (3). Note that M and N are positive integers, M on the input side may be 1, and N on the output side may be 2 or more. However, L shown in the equations 2 and 3 represents the length of the multimode interference waveguide.

[Equation 2]
L = (3 / 4N) Lπ (N is a positive integer) (2)
[Equation 3]

L = (3 / N) Lπ (N is a positive integer) (3)
The first optical waveguide group 1 includes M optical waveguides each having one end connected to each input side port (hereinafter referred to as an input port) of the M × N type multimode interference waveguide 4. The first optical waveguide group 1 has the other end of each optical waveguide as an incident surface. In the present embodiment, in order to explain the 1 × 3 type multimode interference waveguide 4a as an example, the first optical waveguide group 1 includes one optical waveguide (hereinafter referred to as the incident optical waveguide 1a). ). In particular, the incident optical waveguide 1a according to the present embodiment is a linear waveguide composed of only a linear region having a waveguide length of about 50 μm and a waveguide width of about 1.0 μm. In addition, the incident optical waveguide 1 a is connected to the center of the input side of the M × N type multimode interference waveguide 4.

  The second optical waveguide group 2 has one end connected to each port on the output side of the M × N type multimode interference waveguide 4 (hereinafter referred to as a branch port), and the N × M ′ type multimode interference waveguide. 5 of N optical waveguides each having the other end connected to each input port (hereinafter referred to as a multiplexing port). In the second optical waveguide group 2, the length of one of the N optical waveguides is different from the length of the other optical waveguides. That is, one optical waveguide and the other optical waveguide are one or a plurality of optical waveguides, and the second optical waveguide group 2 includes N optical waveguides having two or more different lengths.

  In this embodiment, the second optical waveguide group 2 includes three 1 × 3 type multimode interference waveguides 4a and 3 × 1 type multimode interference waveguides 5a. It consists of an optical waveguide.

  The second optical waveguide group 2 includes a straight waveguide 2a composed only of a straight region, a curved waveguide composed of a straight region and a curved region (first curved waveguide 2b, second curved waveguide 2c), and the like. The waveguide lengths of the respective optical waveguides are different from each other. However, if the optical waveguides are composed of three optical waveguides having two or more different lengths, 2 of the three optical waveguides The waveguide lengths of the two optical waveguides may be the same, and the waveguide lengths of the remaining one optical waveguide may be different.

  The second optical waveguide group 2 includes a straight waveguide 2a and a curved waveguide (a first curved waveguide 2b and a second curved waveguide 2c), but two or more different lengths are used. As long as it is composed of three optical waveguides having a certain length, it is not limited to a combination of a straight waveguide and a curved waveguide. For example, the straight waveguide 2a is formed by a curved waveguide, and three optical waveguides are formed. All the waveguides may be formed of curved waveguides. In particular, when the waveguide length is changed to a curved waveguide having the same waveguide length with respect to the straight waveguide 2a, the region length of the optical phase matching region 20 is shortened, and the total length of the waveguide type optical filter 100 element is shortened. Can do. Further, the second optical waveguide group 2 may be an optical waveguide including a bent region instead of the curved waveguide. However, since a propagation loss of light due to radiation of the propagation light in the bent region occurs, the curved optical waveguide group 2 may be used. It is preferable to use a waveguide.

  As shown in FIG. 1A, the second optical waveguide group 2 includes a straight waveguide 2a, a first waveguide between the 1 × 3 type multimode interference waveguide 4a and the 3 × 1 type multimode interference waveguide 5a. The curved waveguide 2b and the second curved waveguide 2c are juxtaposed, and the first curved waveguide 2b and the second curved waveguide 2c are respectively provided on both sides of the linear waveguide 2a with reference to the straight waveguide 2a. Arranged.

  The straight waveguide 2a is disposed at a position facing the incident optical waveguide 1a via the 1 × 3 type multimode interference waveguide 4a. In particular, since the optical phase matching region 20 has a region length of about 100 μm, the straight waveguide 2 a that matches the region length of the optical phase matching region 20 has a waveguide length of about 100 μm and a waveguide width of 1. It is about 0 μm.

  The first curved waveguide 2b is described later so that the repetition peak interval (hereinafter referred to as the wavelength peak period) Δλ of the transmitted light from the waveguide type optical filter 100 is approximately 13 nm based on Equation 5 described later. Based on Equation 4, the difference Δd between the waveguide length of the first curved waveguide 2b and the waveguide length of the linear waveguide 2a is set to be longer than that of the linear waveguide 2a by about 52 μm. Yes.

  For this reason, as shown in FIG. 1A, the first curved waveguide 2b is formed by coupling a substantially S-shaped curved region having a curvature radius R of about 23 μm at the center of the optical phase matching region 20, and before and after that. This is an optical waveguide having a configuration in which linear regions having a length of about 4 μm are respectively disposed on the 1 × 3 type multimode interference waveguide 4a side and the 3 × 1 type multimode interference waveguide 5a side.

  Similarly to the first curved waveguide 2b, the second curved waveguide 2c is based on the mathematical expression 5 described later, and based on the mathematical expression 4 described later so that the wavelength peak period Δλ is approximately 26 nm. The difference Δd of the waveguide length of the second curved waveguide 2c with respect to the waveguide length is set to be longer than that of the straight waveguide 2a by about 27 μm.

  For this reason, as shown in FIG. 1A, the second curved waveguide 2c combines a substantially S-shaped curved region having a radius of curvature R of approximately 12 μm at the center of the optical phase matching region 20, and before and after that. This is an optical waveguide having a configuration in which linear regions having a length of about 26 μm are respectively disposed on the 1 × 3 type multimode interference waveguide 4a side and the 3 × 1 type multimode interference waveguide 5a side.

  The third optical waveguide group 3 includes M ′ optical waveguides each having one end connected to each port on the output side of the N × M′-type multimode interference waveguide 5 (hereinafter referred to as an output port). The third optical waveguide group 3 has the other end of each optical waveguide as an exit surface. In the present embodiment, in order to explain the 3 × 1 type multimode interference waveguide 5a as an example, the third optical waveguide group 3 includes one optical waveguide (hereinafter referred to as an output optical waveguide 3a). ). In particular, the output optical waveguide 3a according to the present embodiment is a linear waveguide having only a linear region with a waveguide length of about 50 μm and a waveguide width of about 1.0 μm.

The incident optical waveguide 1a, the 1 × 3 type multimode interference waveguide 4a, the straight waveguide 2a, the first curved waveguide 2b, the second curved waveguide 2c, the 3 × 1 type multimode interference waveguide 5a, and The outgoing optical waveguide 3a is a high-mesa waveguide having the same layer structure. These cross-sectional structure, as shown in FIG. 2, the Si substrate on the substrate layer 10 to the substrate, the core layer 12 consisting of the first cladding layer 11, Si consisting of SiO _2, and the SiO ₂ Each of the second cladding layers 13 is a high mesa structure in which each is laminated. In particular, in the present embodiment, the thickness of the first cladding layer 11 is about 1 μm, the thickness of the core layer 12 is about 0.3 μm, and the thickness of the second cladding layer 13 is about 1 μm. is there.

In addition, the layer structure according to the present embodiment has a SiO ₂ / Si / SiO ₂ structure as a material system of the optical waveguide, but is not limited to this material system, and may be, for example, an InP semiconductor material. Even a LiNbO ₃ -based material is applicable.

  The waveguide type optical filter 100 according to the present embodiment includes an incident optical waveguide 1a, a 1 × 3 type multimode interference waveguide 4a, a straight waveguide 2a, a first curved waveguide 2b, and a second curved waveguide. Although the 2c, 3 × 1 type multimode interference waveguide 5a and the output optical waveguide 3a are high mesa waveguides, the layer structure is not limited, and a ridge structure or a buried structure is also applicable.

Hereinafter, the principle that a small optical filter can be realized by the waveguide type optical filter 100 according to the present embodiment will be described.
In general, the light of wavelength λ ₀ that is N-branched in the multimode interference waveguide has the same amplitude and is output with a phase determined relatively between the branch ports.

  For example, in the 1 × 3 type multimode interference waveguide 4a according to the present embodiment, in the branch port on the three output side, when the phase of light output from the center branch port is set to 0, the center branch is obtained. The phase of light output from the two branch ports located outside the port is π / 3.

  Therefore, when the N-branched light is multiplexed again by the N × M ′ type multimode interference waveguide 5, even if the amplitudes of the light propagating through all N optical waveguides are equal, If the signals are not input with a relatively fixed phase between the multiplexing ports of the N × M ′ type multimode interference waveguide 5, the N × M ′ type multimode interference waveguide 5 can be used for reliable multiplexing. However, part or most of the light is emitted from the N × M ′ type multimode interference waveguide 5.

  That is, when light is not input to each multiplexing port of the N × M ′ type multimode interference waveguide 5 with a relatively determined phase, optical loss occurs, and the light completely passes through the waveguide type optical filter 100. Means that it will not pass through. Therefore, when the N-branched light using the M × N type multimode interference waveguide 4 is multiplexed by the N × M ′ type multimode interference waveguide 5, the optical phase matching region 20 is used for input. It is necessary to input light to the N × M ′ type multimode interference waveguide 5 with a phase determined relatively between the respective multiplexing ports.

  In the 3 × 1 type multimode interference waveguide 5a according to the present embodiment, when the phase of the light input to the central multiplexing port is set to 0 in the multiplexing port on the three input side, the center The phase at the two multiplexing ports located outside the multiplexing port may be input as 5π / 3.

  Specifically, light output from two branch ports located outside the central branch port in each branch port of the 1 × 3 type multimode interference waveguide 4a is converted into 3 × 1 type multimode interference waveguide 5a. In order to reach two multiplex ports located outside the central multiplex port at each port, the linear guide is such that the phase difference from the light input to the central multiplex port is 5π / 3. This phase difference can be obtained by making both the first curved waveguide 2b and the second curved waveguide 2c longer than the waveguide 2a.

Here, among the plurality of optical waveguides arranged in parallel from each branch port of the multimode interference waveguide, the waveguide length of the optical waveguide outside the central optical waveguide with respect to the waveguide length of the central optical waveguide Is expressed by the following equation (4). Where n _eq is the equivalent refractive index of the optical waveguide in the optical phase matching region, Φ ₀ is the initial matching phase, and m is an integer.

[Equation 4]
Δd = λ ₀ (Φ ₀ + 2π (m−1)) / 2πn _eq (4)

In the present embodiment, as described above, in the branch port on the 3 output side of the 1 × 3 type multimode interference waveguide 4a, the phase of the light output from the center branch port is set to 0. The phase of the light output from the two branch ports located outside the central branch port is π / 3, and the multiplexing port on the three input side of the 3 × 1 type multimode interference waveguide 5a When the phase of light input to the central multiplexing port is 0, the phase at the two multiplexing ports located outside the central multiplexing port is 5π / 3, The initial matching phase Φ ₀ is given by Φ ₀ = 3π / 5−π / 3.

Here, referring to Equation 4, the difference Δd between the waveguide lengths of the first curved waveguide 2b and the second curved waveguide 2c with respect to the waveguide length of the straight waveguide 2a is not necessarily limited to one value. It turns out that it is not a function of m. This means that Δd, which is the same value as Δd in an integer m, can be realized by an integer m ′ different from the integer m and a wavelength λ ′ different from the wavelength λ ₀ .

  That is, it can be seen that the waveguide type optical filter 100 according to the present invention is a wavelength filter having a certain FSR (Free Spectral Range). When this FSR is a wavelength peak period Δλ, the wavelength peak period Δλ is expressed by the following equation (5).

[Equation 5]
Δλ = λ ₀ / m (5)

Thus, the waveguide type optical filter 100 according to the present invention has a feature that the wavelength peak period Δλ can be freely set according to the principle described above.
Here, in the present embodiment, the first curved waveguide 2b and the second curved waveguide 2c have different waveguide lengths. However, the first curved waveguide 2b and the second curved waveguide 2c are assumed to be different. When the waveguide length of the curved waveguide 2c is the same length and is designed so as to satisfy the equations 4 and 5, the transmission spectrum thereof is, for example, FIG. 3 (a) and FIG. As shown in b).

  FIG. 3A shows the waveguide type light when the waveguide length of the first curved waveguide 2b (second curved waveguide 2c) is set so that the wavelength peak period Δλ is about 26 nm. It is a transmission spectrum by the filter 100, a horizontal axis is wavelength [nm], and a vertical axis | shaft is the transmittance | permeability. FIG. 3B shows the waveguide type light when the waveguide length of the first curved waveguide 2b (second curved waveguide 2c) is set so that the wavelength peak period Δλ is about 13 nm. It is a transmission spectrum by the filter 100, a horizontal axis is wavelength [nm], and a vertical axis | shaft is the transmittance | permeability.

  As shown in FIGS. 3 (a) and 3 (b), the first curved waveguide 2b and the second curved waveguide 2c are designed so as to satisfy the equations (4) and (5). As the type optical filter 100, transmission spectra having different wavelength peak periods Δλ can be freely realized.

  On the other hand, the line width of one transmission peak of the transmission spectrum and the wavelength peak period Δλ are directly correlated, and if the line width of the transmission peak is narrowed, the wavelength peak period Δλ also becomes narrow simultaneously. In particular, when the waveguide lengths of the first curved waveguide 2b and the second curved waveguide 2c are the same, the waveguide is used as a local area network that is expected to be used in a wide wavelength range. Application of the mold light filter 100 is difficult.

  Therefore, the waveguide type optical filter 100 according to the present embodiment further has the following operation principle.

  Usually, as described above, when individually designing the wavelength peak period Δλ and the line width of one transmission peak, several optical filters having different transmission characteristics are connected in series (subordinate connection), A desired transmission characteristic can be designed as a product of the transmission characteristics. For example, the Mach-Zehnder type and ladder type optical filters described in the background art are typical examples.

  In the present invention, similarly to the Mach-Zehnder type or ladder type optical filter, a wavelength filter having a wavelength peak period Δλ of 26 nm and a wavelength filter having a wavelength peak period Δλ of 13 nm are connected in a subordinate manner in the waveguide direction. If integrated, the transmission characteristics shown in FIG. 4B are obtained as the product of the transmission characteristics of the two wavelength filters shown in FIG. That is, in the transmission characteristics shown in FIG. 4B, a transmission spectrum having a narrow line width is obtained as the line width at the center wavelength although the wavelength peak period Δλ is approximately 26 nm. This is because the peak or valley due to the transmission peak in the wavelength filter having a wavelength peak period Δλ of 26 nm and the valley or peak due to the transmission peak in the wavelength filter having a wavelength peak period Δλ of 13 nm are combined to reduce the transmission peak, This is the result of suppressing the mode. In FIG. 4A, the solid line indicates the transmission characteristic of the wavelength filter having a wavelength peak period Δλ of 13 nm, and the broken line indicates the transmission characteristic of a wavelength filter having a wavelength peak period Δλ of 26 nm. In FIGS. 4A and 4B, the horizontal axis is the wavelength [nm], and the vertical axis is the transmittance.

  However, when performing such a subordinate connection, it is necessary to connect a plurality of wavelength filters in series in the waveguide direction, and the length of the waveguide type optical filter 100 is inevitably increased. There is a problem, which is not preferable from the viewpoint of miniaturization and cost reduction of the waveguide type optical filter 100.

  In the waveguide type optical filter 100 according to this embodiment, in order to solve this conventional problem, the first curved waveguide 2b and the second curved waveguide 2c have different waveguide lengths. From the recent research results of the inventors, it has been found that the transmission characteristics shown in FIG. 4B can be realized without connecting a plurality of wavelength filters.

  Therefore, in the waveguide type optical filter 100 according to this embodiment, a product of a plurality of different transmission spectra can be realized without increasing the total length of the waveguide type optical filter 100, and the wavelength peak period Δλ and the line width In addition to this free setting, it is possible to realize miniaturization and cost reduction of the waveguide type optical filter 100, which has been difficult to achieve with the prior art.

Next, with reference to FIG. 5 and FIG. 6, a method for manufacturing the waveguide type optical filter 100 according to the present embodiment will be described.
First, an SiO ₂ film 40 is deposited on a normal SOI (Silicon on Insulator) substrate 30 by using a thermal CVD (Chemical Vapor Deposition) method (FIG. 5A).

  Then, by using a photolithography method by a stepper (reduction projection exposure apparatus), the first optical waveguide group 1, the M × N type multimode interference waveguide 4, and the second optical waveguide group shown in FIG. 2. An etching mask 50 is formed in accordance with the planar shapes of the N × M ′ type multimode interference waveguide 5 and the third optical waveguide group 3 (FIG. 5B).

Using this mask 50, dry etching is performed by an ICP (Inductively Coupled Plasma) method, and the SiO ₂ film 40 to be the second cladding layer 13, the Si layer of the SOI substrate 30 to be the core layer 12, Then, unnecessary portions in the SiO ₂ layer of the SOI substrate 30 to be the first cladding layer 11 are removed, and a high mesa structure is formed as a cross-sectional shape (FIG. 6A). In FIG. 6A, the etching progresses to the surface of the substrate layer 10 of the SOI substrate 30 and a part thereof is removed, and the etching bottom surface 10 c is illustrated on the substrate layer 10.
Thereafter, the mask 50 immediately above the second cladding layer 13 is removed by an organic solvent and an ashing method (FIG. 6B).

  Then, the structure shown in FIGS. 1A and 2 is formed by cleaving the substrate 10 on which a plurality of waveguide type optical filter 100 elements are formed along the boundary between the waveguide type optical filter 100 elements. A waveguide-type optical filter 100 element having the following can be obtained. By this cleavage, the rear end face (one end face 10a of the substrate 10 and the incident face of the incident optical waveguide 1a) and the front end face (the other end face 10b of the substrate 10 and the outgoing face of the outgoing optical waveguide 3a) are formed. Each is formed.

  Finally, an antireflection film is formed on each of the front end face and the rear end face, and the manufacture of the waveguide type optical filter 100 element is completed. In the case of the waveguide type optical filter 100 shown in FIG. 1B, an antireflection film is formed on the front end face (one end face 10a of the substrate 10 and the incident face of the incident optical waveguide 1a), and the rear end face (substrate). 10 is formed on the other end face 10b of 10 and the exit face of the second optical waveguide group 2, and the manufacture of the waveguide type optical filter 100 element is completed.

  In the manufacturing method according to the present embodiment, a stepper is used for the photolithography method, but the present invention is not necessarily limited to this. For example, an electron beam exposure apparatus can be applied.

In the manufacturing method according to the present embodiment, the thermal CVD method is used for forming the SiO ₂ film 40. However, for example, the plasma CVD method or the sputtering method can be applied.

  Further, in the manufacturing method according to the present embodiment, the manufacturing process of the high mesa structure is not limited to the ICP method. For example, an NLD (magnetic neutral loop discharge) method or an RIE (Reactive Ion Etching) is used. Even the law is applicable.

  Furthermore, in the manufacturing method according to the present embodiment, a high-mesa structure in which the progress of etching reaches the substrate layer 10 is used, but it is not always necessary to etch the substrate layer 10 and the SOI substrate that becomes the core layer 12 is used. It is sufficient that 30 Si layers are etched, and for example, a mesa structure may be used.

  In the manufacturing method according to the present embodiment, the formation of the rear end face and the front end face of the waveguide type optical filter 100 element is not necessarily cleaved, for example, after the waveguide type optical filter 100 element is cut out. You may grind | polish and you may give a coating etc. to the back end surface and front end surface of the cut-out waveguide type optical filter 100 element.

  As described above, the waveguide type optical filter 100 according to this embodiment includes N (N is 3 or more) between the M × N type multimode interference waveguide 4 and the N × M ′ type multimode interference waveguide 5. Of the second optical waveguide group 2, and the length of one optical waveguide of the second optical waveguide group 2 is different from the length of the other optical waveguide, thereby causing a wavelength peak. The period Δλ can be freely set, and there is an effect that a certain FSR can be provided.

  In particular, conventional Mach-Zehnder type and ladder type optical filters depend on optical filters having the same transmission characteristics in order to increase the ratio of transmitted light to non-transmitted light (narrow the line width of the transmission peak). It was necessary to connect (for example, two stages).

  On the other hand, the waveguide type optical filter 100 according to the present embodiment includes two or more types of the second optical waveguide group 2 (for example, two linear waveguides 2a and two waveguides having the same waveguide length). By using an optical waveguide of two types with the first curved waveguide 2a), the line width of the transmission peak is the same as that of the subordinate connection (for example, two stages) using the conventional Mach-Zehnder type and ladder type optical filters. Can be narrowed. In addition, the waveguide-type optical filter 100 does not require multistage subordinate connections, and has an operational effect that an optical filter having a relatively simple configuration can be realized.

  Further, when the waveguide type optical filter 100 is applied to a local area network assumed to be used in a wide wavelength range, the second optical waveguide group 2 has N lengths having three or more different lengths. By using the optical waveguide, it is possible to achieve the same effect as the integration of different bandpass filters without increasing the size of the optical filter.

  In the waveguide type optical filter 100 according to the present embodiment, the radius of curvature R in the substantially S-curved region of the first curved waveguide 2b is 23 μm, and the substantially S-shaped curve of the second curved waveguide 2c. Although the radius of curvature R in the region is 12 μm, the radius of curvature is not limited to this radius as long as a desired waveguide length difference Δd can be realized.

In addition, although the incident optical waveguide 1a and the outgoing optical waveguide 3a according to the present embodiment are linear waveguides, they are not necessarily linear waveguides. For example, a spot size conversion function by a taper structure or the like can be provided. A structure that increases the optical coupling efficiency with the optical fiber may be provided.
Moreover, the waveguide type optical filter 100 according to the present embodiment does not necessarily deny the subordinate connection, and there is no problem even if the subordinate connection is used in combination.

  The waveguide type optical filter 100 according to the present embodiment includes a 1 × 3 type multimode interference waveguide 4 a and an M × N type multimode interference waveguide 4 and an N × M ′ type multimode interference waveguide 5. The 3 × 1 type multimode interference waveguide 5a has been described as an example. For example, the 1 × 4 type multimode interference waveguide 4 and the 4 × 1 type multimode interference waveguide 5 illustrated in FIG. The 1 × 5 type multimode interference waveguide 4 and the 5 × 1 type multimode interference waveguide 5 shown in FIG.

  7A includes a 1 × 3 type multimode interference waveguide 4 and a 3 × 1 type multimode interference waveguide 5, and the second optical waveguide group 2 includes: It is composed of one linear waveguide 2a and two first curved waveguides 2b having the same waveguide length, and is composed of three optical waveguides having two different lengths. Further, in the waveguide type optical filter 100 shown in FIG. 7B, the second optical waveguide group 2 has the same waveguide length 2 as the two straight waveguides 2a having the same waveguide length. The first curved waveguide 2b is composed of four optical waveguides having two different lengths. In addition, in the waveguide type optical filter 100 shown in FIG. 7C, the second optical waveguide group 2 has two first curved waveguides having the same waveguide length as the one straight waveguide 2a. The waveguide 2b and the two second curved waveguides 2c having the same waveguide length are composed of five optical waveguides having three different lengths.

  Each waveguide type optical filter 100 shown in FIG. 7 increases the number of optical waveguides in the second optical waveguide group 2 in the optical phase matching region 20 as shown in FIG. It turns out that the filter effect by increases. In FIG. 8, the solid line shows the transmission characteristics of the waveguide type optical filter 100 shown in FIG. 7C, the broken line shows the transmission characteristics of the waveguide type optical filter 100 shown in FIG. These show the transmission characteristics of the waveguide type optical filter 100 shown in FIG. In FIG. 8, the horizontal axis represents the wavelength [nm], and the vertical axis represents the transmittance [%].

  In particular, the waveguide type optical filter 100 includes an M × N type multimode interference waveguide 4 and an N × M ′ type multimode interference waveguide 5, and a 1 × 9 type multimode interference waveguide shown in FIG. By using the 4 and 9 × 1 type multimode interference waveguide 5, as shown in FIGS. 9B and 9C, the side mode suppression ratio (SMSR = (adjacent to the center wavelength)). Matching peak power) / (peak power at center wavelength)) achieves 0.29, and good single mode operation can be achieved.

  In the waveguide type optical filter 100 shown in FIG. 9A, the second optical waveguide group 2 includes two first curved waveguides having the same waveguide length as the one linear waveguide 2a. The waveguide 2b, the two second curved waveguides 2c having the same waveguide length, the two third curved waveguides 2d having the same waveguide length, and the waveguide lengths 2 are the same. The fourth curved waveguide 2e is composed of nine optical waveguides having five different lengths. In FIG. 8B, the horizontal axis represents wavelength [nm], and the vertical axis represents transmittance [%]. In FIG. 8C, the horizontal axis represents the number N of optical waveguides in the second optical waveguide group 2, and the vertical axis represents the submode suppression ratio.

Furthermore, in the waveguide type optical filter 100 according to the present embodiment, the first optical waveguide group 1, the second optical waveguide group 2, the third optical waveguide group 3, and the M × N type multimode interference waveguide 4. Also, compensation of optical loss can be realized by activating a part of the N × M ′ type multimode interference waveguide 5 with a layer structure having an active layer between PN junctions. That is, in this layer structure, a forward bias is applied between the PN junctions, holes and electrons are confined in the active layer, and light that is lost while propagating through the optical waveguide is compensated by light that is recombined and emitted. There is an effect of being able to.
(Second embodiment of the present invention)
FIG. 10A is a plan view showing an example of a schematic configuration of the waveguide type optical filter according to the second embodiment, and FIG. 10B is an arrow of the waveguide type optical filter shown in FIG. It is sectional drawing of a view CC 'line. 10, the same reference numerals as those in FIGS. 1 to 9 denote the same or corresponding parts, and the description thereof is omitted.

  The 1 × 1 type multimode interference waveguide 6 is a multimode interference waveguide having one input and one output. In particular, the 1 × 1 type multimode interference waveguide 6 according to this embodiment has a substantially rectangular interference region having a waveguide length of about 120 μm and a waveguide width of about 6.5 μm.

  The optical phase matching region 20a is a 1 × 1 type multi-channel at substantially the center of the linear waveguide 2a, the first curved waveguide 2b, and the second curved waveguide 2c in the optical phase matching region 20 according to the first embodiment. This is a region where the mode interference waveguide 6 is inserted. For this reason, the region length of the optical phase matching region 20a is obtained by adding about 120 μm of the waveguide length of the 1 × 1 type multimode interference waveguide 6 to the region length of about 100 μm of the optical phase matching region 20 according to the first embodiment. About 220 μm.

  The 1 × 1 type multimode interference waveguide 6 inserted approximately at the center of each of the straight waveguide 2a and the first curved waveguide 2b has the same waveguide length. The difference Δd in the waveguide length of the first curved waveguide 2b with respect to the waveguide length and the wavelength peak period Δλ are the same as those in the first embodiment (Δd = 52 μm, Δλ = 13 nm). Similarly, since the 1 × 1 type multimode interference waveguide 6 inserted approximately at the center of each of the straight waveguide 2a and the second curved waveguide 2c has the same waveguide length, The difference Δd in the waveguide length of the second curved waveguide 2c with respect to the waveguide length and the wavelength peak period Δλ are the same as in the first embodiment (Δd = 26 μm, Δλ26 nm).

The 1 × 1 type multimode interference waveguide 6 includes an incident optical waveguide 1a, a 1 × 3 type multimode interference waveguide 4a, a straight waveguide 2a, a first curved waveguide 2b, and a second curved waveguide 2c. The 3 × 1 type multimode interference waveguide 5a and the output optical waveguide 3a have the same layer structure and are high-mesa waveguides. That is, as shown in FIG. 10B, the cross-sectional structure of the 1 × 1 type multimode interference waveguide 6 is such that the first clad layer 11 made of SiO _{2 is formed} on the substrate layer 10 based on the Si substrate. The core layer 12 made of Si, and the second cladding layer 13 made of SiO ₂ have a high mesa structure, respectively.

  The second embodiment is different from the first embodiment only in that the 1 × 1 type multimode interference waveguide 6 is provided, except for the operational effects of the 1 × 1 type multimode interference waveguide 6. The same effects as those of the first embodiment are achieved.

  In the waveguide type optical filter 100 according to the present embodiment, since the wavelength components other than the center wavelength are further cut by the 1 × 1 type multimode interference waveguide 6, the application to the local area network is particularly considered. In such a case (for example, filtering is necessary between the 1.3 μm band and the 1.55 μm band which are largely separated from each other), the effect of further suppressing the crosstalk is obtained.

(Third embodiment of the present invention)
FIG. 11A is a plan view showing an example of a schematic configuration of the semiconductor laser according to the third embodiment, and FIG. 11B is another example of the schematic configuration of the semiconductor laser according to the third embodiment. FIG. 12A is a cross-sectional view taken along the line DD ′ of the semiconductor laser shown in FIG. 11, and FIG. 12B is a cross-sectional view taken along the line EE ′ of the semiconductor laser shown in FIG. is there. FIG. 13 is an explanatory diagram for explaining a method of manufacturing a semiconductor laser according to the third embodiment, and FIG. 13A is a MOVPE corresponding to a cross-sectional view taken along the line DD ′ of the semiconductor laser shown in FIG. FIG. 13B is a cross-sectional view in a state in which a mask corresponding to the cross-sectional view taken along the line DD ′ of the semiconductor laser shown in FIG. 11 is formed. . FIG. 14 is an explanatory diagram for explaining a method of manufacturing a semiconductor laser according to the third embodiment, and FIG. 14A is an etching corresponding to a cross-sectional view taken along the line DD ′ of the semiconductor laser shown in FIG. 14B is a cross-sectional view in a state in which a high mesa structure is formed, and FIG. 14B is a cross-sectional view in a state embedded in BCB corresponding to the cross-sectional view taken along the line DD ′ of the semiconductor laser shown in FIG.

  In the semiconductor laser 200, an optical waveguide and a multimode interference waveguide are disposed on a substrate 210, and a forward bias is applied between internal PN junctions so that holes and electrons are confined in an active layer and recombined. The emitted light is branched, the phases of the light are matched, and the light is combined and emitted to the outside. Therefore, the semiconductor laser 200 separates light emitted on the one end face 210a side of the substrate 210 when the end face of the optical waveguide on the other end face 210b side facing the one end face 210a of the substrate 210 is the exit face. It is necessary to provide multimode interference waveguides for wave and multiplexing respectively. In this case, the semiconductor laser 200 includes a first optical waveguide group 201, a second optical waveguide group 202, a third optical waveguide group 203, an M × N type multimode interference waveguide 204, and an N ×, which will be described later. At least an M′-type multimode interference waveguide 205 is provided (see, for example, FIG. 11B).

  Further, the semiconductor laser 200 uses the end face of the optical waveguide on the other end face 210b side of the substrate 210 as a reflection surface for the light emitted on the one end face 210a side of the substrate 210, and the optical waveguide on the one end face 210a side of the substrate 210. When the end face is used as the exit face, a multi-mode interference waveguide that is used for both demultiplexing and multiplexing may be provided. In this case, the semiconductor laser 200 includes at least a first optical waveguide group 201, a second optical waveguide group 202, and an M × N type multimode interference waveguide 204 (for example, see FIG. 11A).

  In this embodiment, for the light emitted on the one end surface 210a side of the substrate 210, the end surface of the optical waveguide on the other end surface 210b side of the substrate 210 is used as a reflection surface, and the optical waveguide on the one end surface 210a side of the substrate 210 is used. The case where the end face of the substrate 210 is used as the exit face will be described as an example. However, the semiconductor uses the light emitted from the one end face 210a side of the substrate 210 as the exit face of the optical waveguide on the other end face 210b side of the substrate 210. The laser 200 may be used.

  As shown in FIG. 11A, the semiconductor laser 200 according to this embodiment includes a first optical waveguide group 201, an M × N type multimode interference waveguide 204, and an optical phase matching region on a substrate 210. 220 and the second optical waveguide group 202 as the optical waveguide region 221 are integrated. In particular, the semiconductor laser 200 according to this embodiment includes the first optical waveguide group 101, the M × N type multimode interference waveguide 204, and the second optical waveguide between the one end surface 210a and the other end surface 210b of the substrate 210. The waveguide group 202 constitutes a resonator.

  The M × N type multi-mode interference waveguide 204 is a multi-mode interference waveguide having M (M is an integer of 1 or more) input and N (N is an integer of 3 or more) output. In the present embodiment, the 1 × 3 type multimode interference waveguide 204a in which M is 1 and N is 3 will be described as an example. However, the present embodiment is limited to this 1 × 3 type multimode interference waveguide 204a. It is not something that can be done. In particular, the 1 × 3 type multimode interference waveguide 204a according to the present embodiment has a waveguide length along the light guiding direction (hereinafter referred to as a waveguide length) of about 280 μm, and the waveguide width. Has a substantially rectangular interference region of about 20 μm.

  The multimode interference waveguide can be designed using a known technique. For example, based on the MMI theory, the M × N type multimode interference waveguide 204 is the same as described in the first embodiment. Can be designed to

  The first optical waveguide group 201 includes M optical waveguides each having one end connected to each port on the input side of the M × N type multimode interference waveguide 204 (hereinafter referred to as an input port). Each optical waveguide of the optical waveguide group 201 is a single mode waveguide. Further, the first optical waveguide group 201 has the other end of each optical waveguide as an emission surface.

  In the present embodiment, the first optical waveguide group 201 includes a single optical waveguide 201a in order to describe the 1 × 3 type multimode interference waveguide 204a as an example. In particular, the optical waveguide 201a according to the present embodiment is a linear waveguide composed of only a linear region having a waveguide length of about 50 μm and a waveguide width of about 2.0 μm. The optical waveguide 201a is connected to the input side of the M × N type multimode interference waveguide 204 at substantially the center.

  The second optical waveguide group 202 is connected to each port on the output side of the M × N type multimode interference waveguide 204 (hereinafter referred to as an output port), and N ends having three or more different lengths. It consists of an optical waveguide. The second optical waveguide group 202 uses the other end of each optical waveguide as a reflection surface.

In the present embodiment, the second optical waveguide group 202 includes three optical waveguides in order to explain the 1 × 3 type multimode interference waveguide 204a as an example.
The second optical waveguide group 202 can be divided into an optical phase matching region 220 and an optical waveguide region 221, and a straight waveguide 202a composed of only a straight region and a curved waveguide composed of a straight region and a curved region (first The second curved waveguide 202b and the second curved waveguide 202c). In the second optical waveguide group 202, each optical waveguide is a single mode waveguide, and the waveguide lengths of the respective optical waveguides are different from each other.

  The second optical waveguide group 202 includes a straight waveguide 202a and a curved waveguide (a first curved waveguide 202b and a second curved waveguide 202c), but has three or more different lengths. Is not limited to a combination of a straight waveguide and a curved waveguide, and for example, the straight waveguide 202a in the optical phase matching region 220 is formed by a curved waveguide. All of the three optical waveguides in the optical phase matching region 220 may be configured by curved waveguides. In particular, when the waveguide phase is changed to a curved waveguide having the same waveguide length with respect to the linear waveguide 202a in the optical phase matching region 220, the length of the optical phase matching region 220 is shortened, and the total length of the semiconductor laser 200 element is reduced. Can be shortened. Further, the second optical waveguide group 202 may be an optical waveguide including a bent region instead of the curved waveguide in the optical phase matching region 220. However, there is a light propagation loss due to the propagation of propagating light in the bent region. In order to occur, it is preferable to use a curved waveguide.

  As shown in FIG. 11A, the second optical waveguide group 202 includes a straight waveguide 202a and a first curved waveguide between the 1 × 3 type multimode interference waveguide 204a and the other end face 210b of the substrate 110. 202b and the second curved waveguide 202c are juxtaposed, and the first curved waveguide 202b and the second curved waveguide 202c are respectively disposed on both sides of the linear waveguide 202a with reference to the straight waveguide 202a. .

  The straight waveguide 202a is disposed at a position facing the optical waveguide 201a via the 1 × 3 type multimode interference waveguide 204a. In particular, since the optical phase matching region 220 has a region length of about 50 μm and the optical waveguide region 221 has a region length of about 50 μm, the linear waveguide matches the region lengths of the optical phase matching region 220 and the optical waveguide region 221. 202a has a waveguide length of about 100 μm and a waveguide width of about 2.0 μm.

  In the first curved waveguide 202b, the interval between repeated peaks of transmitted light from the semiconductor laser 200 (hereinafter referred to as a wavelength peak period) Δλ is approximately 13 nm based on Equation 5 described above in the first embodiment. Further, based on Equation 4 described above in the first embodiment, the difference Δd in the waveguide length of the first curved waveguide 202b with respect to the waveguide length of the linear waveguide 202a is approximately 26 μm (approximately 52 μm in the round trip). The length is set to be longer than that of the waveguide 202a.

  For this reason, the first curved waveguide 202b in the optical phase matching region 220 has a substantially S-shaped curved region having a radius of curvature R of about 23 μm as shown in FIG. The optical waveguide has a configuration in which a linear region having a length of about 4 μm is disposed in front of the waveguide region 221 (on the 1 × 3 type multimode interference waveguide 204a side).

  Similarly to the first curved waveguide 202b, the second curved waveguide 202c is configured so that the wavelength peak period Δλ is approximately 26 nm based on the above-described Equation 5 in the first embodiment. The difference Δd in the waveguide length of the second curved waveguide 202c with respect to the waveguide length of the linear waveguide 202a is about 13.5 μm (about 27 μm in the reciprocation) than that of the linear waveguide 202a. The length is set to be long.

  For this reason, as shown in FIG. 11A, the second curved waveguide 202c in the optical phase matching region 220 has a substantially S-shaped curved region having a radius of curvature R of about 12 μm. The optical waveguide has a configuration in which a linear region having a length of about 26 μm is disposed in front of the waveguide region 221 (on the 1 × 3 type multimode interference waveguide 204a side).

  The straight waveguide 202a, the first curved waveguide 202b, and the second curved waveguide 202c in the optical waveguide region 221 have a waveguide length of about 50 μm and a waveguide width of about 2.0 μm. It is a linear waveguide consisting of

  The optical waveguide 201a, the 1 × 3 type multimode interference waveguide 204a, the straight waveguide 202a, the first curved waveguide 202b, and the second curved waveguide 202c have the same layer structure, and are high mesa waveguides. is there.

  Further, as shown in FIG. 12, these cross-sectional structures include a buffer layer 211 made of n-InP which is an n-type semiconductor, a long wavelength band (1. A light emitting layer 212 made of InGaAsP / InGaAsP serving as an active layer for realizing a semiconductor laser of a 55 μm band), a first cladding layer 213 made of i-InP which is an intrinsic semiconductor, and a second made of p-InP which is a p-type semiconductor. The clad layer 214 and the contact layer 215 made of p-InGaAs, which is a p-type semiconductor, each have a high mesa structure. For the high mesa structure, BCB (benzocyclobutene), which is a low dielectric constant organic film, is buried in the non-waveguide region, and the buried layer 216 is formed.

  As shown in FIG. 12, this high mesa structure has a contact layer 215, a second cladding layer 214, a first cladding layer 213, a light emitting layer 212, and a buffer layer 211 in a non-waveguide region (a region where BCB is embedded). In this structure, a part of the substrate layer 210 is removed by etching.

  The light-emitting layer 212 is a normal light-emitting layer composed of a SCH (Separate Confinement Hetero-structure) and a multi-quantum well (MQW).

  In particular, in this embodiment, the thickness of the buffer layer 211 is about 100 nm, the thickness of the light emitting layer 212 is about 100 nm, the thickness of the first cladding layer 213 is about 100 nm, and the second The cladding layer 214 has a thickness of about 900 nm, and the contact layer 215 has a thickness of about 150 nm.

Next, a method for manufacturing the semiconductor laser 200 according to the present embodiment will be described with reference to FIGS.
First, an n-InP film 230, an InGaAsP / InGaAsP-1.55 μm band film 240, i, and the like are formed on a normal n-InP substrate 210 by using MOVPE (Metal-Organic Vapor Phase Epitaxy). A -InP film 250, a p-InP film 260, and a p-InGaAs film 270 are sequentially deposited to form a stacked layer (FIG. 13A).

  Then, using a normal photolithography method by a stepper (reduction projection exposure apparatus), the first optical waveguide group 201, the M × N type multimode interference waveguide 204, and the second optical waveguide shown in FIG. An etching mask 280 is formed on the p-InGaAs film 270 in accordance with the planar shape of the waveguide group 202 (FIG. 13B).

  Using this mask 280, dry etching is performed by the RIE (reactive ion etching) method, and the p-InGaAs film 270 to be the contact layer 215, the p-InP film 260 to be the second cladding layer 214, the first Unnecessary portions of the i-InP film 250 to be the cladding layer 213, the InGaAsP / InGaAsP-1.55 μm band film 240 to be the light emitting layer 212, and the n-InP film 230 to be the buffer layer 211 are partially formed (a mask is formed). The high mesa structure is formed as a cross-sectional shape (FIG. 14A). In FIG. 14A, the etching progresses to the surface of the substrate 210 and a part thereof is removed, and the etching bottom surface 210 c is illustrated on the substrate 210.

  Thereafter, the portion removed by etching is buried with BCB to form a buried layer 216 (FIG. 14B), and the mask 280 immediately above the contact layer 215 is removed by an organic solvent and an ashing method (FIG. 12). .

  Then, a Ti / Pt / Au layer (not shown) serving as an external electrode for applying a forward bias between the PN junctions is formed on the contact layer 215 by electron beam evaporation. The Ti / Pt / Au layer may be selectively formed only on the contact layer 215 or may be formed on the entire surface of the substrate 210 on the contact layer 215 and the buried layer 216. However, in the case where the Ti / Pt / Au layer is selectively formed only on the contact layer 215, the number of manufacturing steps for patterning increases, and therefore, the Ti / Pt / Au layer is formed on the entire surface of the substrate 210 on the contact layer 215 and the buried layer 216. A Pt / Au layer is preferably formed.

  Thereafter, the back surface of the substrate 210 on which the optical waveguide is not formed is polished, and a Ti / Pt / Au layer (not shown) serving as an external electrode for applying a forward bias between the PN junctions is applied to the entire back surface of the substrate 210 with an electron beam. It is formed by vapor deposition.

  Then, the semiconductor laser 200 element having the structure shown in FIGS. 11A and 12 is formed by cleaving the substrate 210 on which the plurality of semiconductor laser 200 elements are formed along the boundary between the semiconductor laser 200 elements. Can be obtained. By this cleavage, the front end surface (one end surface 210a of the substrate 210, the emission surface of the optical waveguide 201a) and the rear end surface (the other end surface 210b of the substrate 210, the reflection surface of the second optical waveguide group 2) of the semiconductor laser 200 element are respectively obtained. It is formed.

  Finally, an antireflection film is formed on the front end face, and a high reflection film is formed on the rear end face, and the manufacture of the semiconductor laser 200 element is completed. In the case of the semiconductor laser 200 shown in FIG. 11B, the rear end face (one end face 210a of the substrate 210, the reflecting face of the optical waveguide 201a) and the front end face (the other end face 210b of the substrate 210, the second optical waveguide). An antireflection film is formed on each of the emission surfaces of group 2 to complete the manufacture of the semiconductor laser 200 element.

  In the manufacturing method according to the present embodiment, the MOVPE method is used as the crystal growth method. However, the method is not necessarily limited to this. For example, the MBE (Molecular Beam Epitaxy) method may be used. Applicable.

In the manufacturing method according to the present embodiment, the RIE method is used as an etching method, but an ICP method or a wet etching method is also applicable.
Further, in the manufacturing method according to the present embodiment, a stepper is used for the photolithography method, but the present invention is not necessarily limited thereto, and for example, an electron beam exposure apparatus can be applied.

  Further, in the manufacturing method according to the present embodiment, the formation of the rear end face and the front end face of the semiconductor laser 200 element does not necessarily need to be cleaved. For example, the semiconductor laser 200 element may be polished after being cut out. The rear end surface and the front end surface of the cut-out semiconductor laser 200 element may be coated.

  In the third embodiment, the semiconductor laser 200 is different from the first and second embodiments only in the layer structure, and the first embodiment is the same as the first embodiment except for the function and effect of the semiconductor laser 200. The same effects as those of the second embodiment and the second embodiment are obtained.

  In the semiconductor laser 200 according to the present embodiment, all higher-order mode light propagating in the 1 × 3 type multimode interference waveguide 204 is branched into three and converted into single mode light. The converted single mode light passes through the optical phase matching region 220, and then passes through the optical waveguide region 221 and is reflected by the end surface of the second optical waveguide group 202 on the other end surface 210 b side of the substrate 210. The reflected single mode light further propagates through the 1 × 3 type multimode interference waveguide 204 after passing through the optical waveguide region 221 and the optical phase matching region 220, and as laser light on the one end surface 210 a side of the substrate 210. The light is output from the end face of the optical waveguide 201a.

  Further, in the semiconductor laser 200 according to the present embodiment, the phase of the output light can be matched by providing the optical phase matching region 220 on the three output sides of the 1 × 3 type multimode interference waveguide 204a.

  In particular, in the semiconductor laser 200 according to the present example, unlike the first embodiment (in the case of FIG. 1A), the optical phase matching region 220 includes the optical phase matching region 20 according to the first embodiment. It is about half and the 3 × 1 type multimode interference waveguide 5a does not exist.

  In this configuration, the end face of the second optical waveguide group 2 on the other end face 210b side of the substrate 210 is present as a reflecting mirror, and the light is folded at the end face of the second optical waveguide group 2 so that the 1 × 3 type multi This is because the signals are input to the three output sides of the mode interference waveguide 204a.

  That is, the 1 × 3 type multimode interference waveguide 204a according to the present example also serves as the 3 × 1 type multimode interference waveguide 5a in the first embodiment, and the element length of the semiconductor laser 200 is unnecessarily increased. There is no need to do.

  As described above, in the semiconductor laser 200 according to the present embodiment, the optical filter performance similar to that of the first embodiment can be realized, and a mechanism for selecting a single wavelength despite having no grating. This has the effect of obtaining oscillation at a single wavelength. In particular, in the semiconductor laser 200 according to this embodiment, the manufacturing process can be simplified as compared with a conventional semiconductor laser such as a DFB-LD (distributed-feedback laser diode) using a grating. There is an effect that a low-cost light source can be realized.

(Fourth embodiment of the present invention)
FIG. 15A is a plan view showing an example of a schematic configuration of the semiconductor laser according to the fourth embodiment, and FIG. 15B is an arrow FF ′ line of the semiconductor laser shown in FIG. FIG. 15, the same reference numerals as those in FIGS. 1 to 14 denote the same or corresponding parts, and the description thereof will be omitted.

  The electrical separation groove 207 is formed by removing a part of the contact layer 215 so as to cross the length direction of at least one optical waveguide in the first optical waveguide group 201. The electrical separation groove 207 according to this embodiment is disposed in the optical waveguide 201a with a length of about 4 μm from the input port of the 1 × 3 type multimode interference waveguide 204a to the one end surface 210a side of the substrate 210. The electrical separation groove 207 is a region where a modulation signal can be applied independently to the optical waveguide 201a.

Next, a method for manufacturing the semiconductor laser 200 according to the present embodiment will be described with reference to FIG.
In the manufacturing method of the semiconductor laser 200 according to the present embodiment, the buried layer 216 is formed (FIG. 14B), and the mask 280 immediately above the contact layer 215 is removed by an organic solvent and an ashing method (FIG. 14). The process up to 12) is the same as the method for manufacturing the semiconductor laser 200 according to the third embodiment, and thus the description thereof is omitted.

A region to be the electrical separation groove 207 in the contact layer 215 exposed by removing the mask 280 is removed by a wet etching method to form the electrical separation groove 207 (FIG. 15B).
Then, a Ti / Pt / Au layer (not shown) serving as an external electrode for applying a forward bias between the PN junctions is formed on the contact layer 215 by electron beam evaporation.

  Thereafter, the back surface of the substrate 210 on which the optical waveguide is not formed is polished, and a Ti / Pt / Au layer (not shown) serving as an external electrode for applying a forward bias between the PN junctions is applied to the entire back surface of the substrate 210 with an electron beam. It is formed by vapor deposition.

Then, by cleaving the substrate 210 on which the plurality of semiconductor laser 200 elements are formed along the boundary between the semiconductor laser 200 elements, the semiconductor laser 200 element having the structure shown in FIG. 15 can be obtained.
Finally, an antireflection film is formed on the front end face, and a high reflection film is formed on the rear end face, and the manufacture of the semiconductor laser 200 element is completed.

  Note that the fourth embodiment is different from the third embodiment only in that the electrical separation groove 207 is formed, and is the same as the third embodiment except for the function and effect of the electrical separation groove 207. Has an effect.

  The semiconductor laser 200 according to the present embodiment has a structure in which the optical waveguide 201a is electrically separated with a short length of about 50 μm and a modulation signal can be applied only to the electrical separation groove 207. Therefore, it is possible to drastically increase the relaxation oscillation frequency equivalent to that of a difficult short cavity of about several tens of μm, and there is an effect that a light source capable of high-speed and direct modulation can be realized.

DESCRIPTION OF SYMBOLS 1 1st optical waveguide group 1a Incident optical waveguide 2 2nd optical waveguide group 2a Linear waveguide 2b 1st curved waveguide 2c 2nd curved waveguide 2d 3rd curved waveguide 2e 4th curved waveguide 3 3rd optical waveguide group 3a Output optical waveguide 4 M × N type multimode interference waveguide 4a 1 × 3 type multimode interference waveguide 5 N × M ′ type multimode interference waveguide 5a 3 × 1 type multimode interference Waveguide 6 1 × 1 type multimode interference waveguide 10 Substrate, substrate layer 10a One end surface 10b The other end surface 10c Etching bottom surface 11 First cladding layer 12 Core layer 13 Second cladding layer 20 Optical phase matching region 20a Optical phase matching region 20a Region 30 SOI substrate 40 SiO ₂ film 50 Mask 100 Waveguide type optical filter 101 First optical waveguide group 110 Substrate 200 Semiconductor laser 201 First optical waveguide Group 201a optical waveguide 202 second optical waveguide group 202a linear waveguide 202b first curved waveguide 202c second curved waveguide 203 third optical waveguide group 204 M × N-type multimode interference waveguide 204a 1 × 3 Type multimode interference waveguide 205 N × M ′ type multimode interference waveguide 207 Electrical separation groove 210 Substrate, substrate layer 210a One end surface 210b The other end surface 210c Etching bottom surface 211 Buffer layer 212 Light emitting layer 213 First cladding layer 214 First 2 Cladding layer 215 Contact layer 216 Buried layer 220 Optical phase matching region 221 Optical waveguide region 230 n-InP film 250 i-InP film 260 p-InP film 270 p-InGaAs film 280 Mask

Claims (8)

A 1 × N type multimode interference waveguide having one input and N (N is an integer of 3 or more) output;
A first optical waveguide group consisting of one optical waveguide having one end connected to the input side port of the 1 × N type multimode interference waveguide;
The 1 × one for each port on the N-type multi-mode interference waveguide on the output side are connected, respectively, and the second optical waveguide group consisting of N optical waveguides that have a different waveguide lengths three or more kinds,
With
The other end of one optical waveguide of the first optical waveguide group is an entrance surface and an exit surface,
The other end of each optical waveguide of the second optical waveguide group is a reflection surface,
Of the second optical waveguide group, the waveguide length of one optical waveguide is different from the waveguide length of the other optical waveguide a plurality of which have different waveguide lengths two or more,
Transmitted light from the exit surface based on a difference in each waveguide length of a plurality of other waveguides of the second optical waveguide group with respect to a waveguide length of one optical waveguide of the second optical waveguide group There are a plurality of wavelength peak periods Δλ that are intervals between the repeated peaks of
Each integer satisfying the following equation 1 and m, for waveguide length of one optical waveguide of the second optical waveguide group, each waveguide length of another optical waveguide of the plurality of the second optical waveguide group A waveguide type optical filter satisfying the following expression 2 where Δd / 2 is the difference between the two.
[Formula 1]
m = λ ₀ / Δλ
(Where λ _{0 is the} incident light wavelength, Δλ is the wavelength peak period)
[Formula 2]
Δd = λ ₀ (Φ ₀ + 2π (m−1)) / 2πn _eq
(Where n _{eq is} the equivalent refractive index of the optical waveguide of the second optical waveguide group, Φ _{0 is the} initial matching phase) A 1 × N type multimode interference waveguide having one input and N (N is an integer of 3 or more) output;
A first optical waveguide group consisting of one optical waveguide having one end connected to the input side port of the 1 × N type multimode interference waveguide;
The 1 × one for each port on the N-type multi-mode interference waveguide on the output side are connected, respectively, and the second optical waveguide group consisting of N optical waveguides that have a different waveguide lengths three or more kinds,
N × 1 type multimode interference waveguide of N (N is an integer greater than or equal to 3) input and 1 output type, the other end of each optical waveguide of the second optical waveguide group being connected to each port on the input side When,
A third optical waveguide group consisting of one optical waveguide having one end connected to the output side port of the N × 1 type multimode interference waveguide and the other end as an exit surface;
With
The other end of one optical waveguide of the first optical waveguide group is an incident surface,
Of the second optical waveguide group, the waveguide length of one optical waveguide is different from the waveguide length of the other optical waveguide a plurality of which have different waveguide lengths two or more,
Transmitted light from the exit surface based on a difference in each waveguide length of a plurality of other waveguides of the second optical waveguide group with respect to a waveguide length of one optical waveguide of the second optical waveguide group There are a plurality of wavelength peak periods Δλ that are intervals between the repeated peaks of
Each integer satisfying the following equation 3 and m, for waveguide length of one optical waveguide of the second optical waveguide group, each waveguide length of another optical waveguide of the plurality of the second optical waveguide group An optical waveguide filter satisfying the following formula 4 where Δd is Δd.
[Formula 3]
m = λ ₀ / Δλ
(Where λ _{0 is the} incident light wavelength, Δλ is the wavelength peak period)
[Formula 4]
Δd = λ ₀ (Φ ₀ + 2π (m−1)) / 2πn _eq
(Where n _{eq is} the equivalent refractive index of the optical waveguide of the second optical waveguide group, Φ _{0 is the} initial matching phase) In the waveguide type optical filter according to claim 1 or 2,
A waveguide type optical filter, wherein one optical waveguide and / or another optical waveguide of the second optical waveguide group is a curved waveguide including a curved region .   A 1 × N type multimode interference waveguide having one input and N (N is an integer of 3 or more) output;
  A first optical waveguide group consisting of one optical waveguide having one end connected to the input side port of the 1 × N type multimode interference waveguide;
  A second optical waveguide group consisting of N optical waveguides each having one end connected to each port on the output side of the 1 × N type multimode interference waveguide and having three or more different waveguide lengths;
  With
  The other end of one optical waveguide of the first optical waveguide group is an emission surface,
  The other end of each optical waveguide of the second optical waveguide group is a reflection surface,
  The 1 × N type multimode interference waveguide, the first optical waveguide group, and the second optical waveguide group have a layer structure having an active layer,
  Of the second optical waveguide group, the waveguide length of one optical waveguide is different from the waveguide lengths of a plurality of other optical waveguides having two or more different waveguide lengths,
  Transmitted light from the exit surface based on a difference in each waveguide length of a plurality of other waveguides of the second optical waveguide group with respect to a waveguide length of one optical waveguide of the second optical waveguide group There are a plurality of wavelength peak periods Δλ that are intervals between the repeated peaks of
  Each integer satisfying the following equation 5 is m, and the waveguide lengths of a plurality of other optical waveguides of the second optical waveguide group with respect to the waveguide length of one optical waveguide of the second optical waveguide group; A semiconductor laser characterized by satisfying the following formula 6, where Δd / 2 is the difference between the two.
[Formula 5]
m = λ ₀ / Δλ
(However, λ ₀ : Incident light wavelength, Δλ: wavelength peak period)
[Formula 6]
Δd = λ ₀ (Φ ₀ + 2π (m−1)) / 2πn _eq
(However, n _eq : Equivalent refractive index of the optical waveguide of the second optical waveguide group, Φ ₀ : Initial matching phase)   In the semiconductor laser according to claim 4,
  The optical waveguide of the first optical waveguide group has a contact layer connected to an external electrode;
  A part of the contact layer is removed so as to cross the length direction of one optical waveguide of the first optical waveguide group, and the 1 × N type multimode interference is passed through the removed region. A semiconductor laser characterized in that a modulation signal is applied to an optical waveguide of the first optical waveguide group separated from the waveguide.   A 1 × N type multimode interference waveguide having one input and N (N is an integer of 3 or more) output;
  A first optical waveguide group consisting of one optical waveguide having one end connected to the input side port of the 1 × N type multimode interference waveguide;
  A second optical waveguide group consisting of N optical waveguides each having one end connected to each port on the output side of the 1 × N type multimode interference waveguide and having three or more different waveguide lengths;
  N × 1 type multimode interference waveguide of N (N is an integer greater than or equal to 3) input and 1 output type, the other end of each optical waveguide of the second optical waveguide group being connected to each port on the input side When,
  A third optical waveguide group consisting of one optical waveguide having one end connected to the output side port of the N × 1 type multimode interference waveguide and the other end as an exit surface;
  With
  The other end of one optical waveguide of the first optical waveguide group is a reflective surface,
  The 1 × N type multimode interference waveguide, the first optical waveguide group, and the second optical waveguide group have a layer structure having an active layer,
  Of the second optical waveguide group, the waveguide length of one optical waveguide is different from the waveguide lengths of a plurality of other optical waveguides having two or more different waveguide lengths,
  Transmitted light from the exit surface based on a difference in each waveguide length of a plurality of other waveguides of the second optical waveguide group with respect to a waveguide length of one optical waveguide of the second optical waveguide group There are a plurality of wavelength peak periods Δλ that are intervals between the repeated peaks of
  Each integer satisfying the following formula 7 is m, and the waveguide lengths of a plurality of other optical waveguides of the second optical waveguide group with respect to the waveguide length of one optical waveguide of the second optical waveguide group; A semiconductor laser characterized by satisfying the following formula 8, where Δd is Δd.
[Formula 7]
m = λ ₀ / Δλ
(However, λ ₀ : Incident light wavelength, Δλ: wavelength peak period)
[Formula 8]
Δd = λ ₀ (Φ ₀ + 2π (m−1)) / 2πn _eq
(However, n _eq : Equivalent refractive index of the optical waveguide of the second optical waveguide group, Φ ₀ : Initial matching phase) In the semiconductor laser according to claim 6,
The optical waveguide of the third optical waveguide group has a contact layer connected to an external electrode;
A part of the contact layer is removed so as to cross the length direction of one optical waveguide of the third optical waveguide group, and the 1 × N type multimode interference is passed through the removed region. the semiconductor laser according to claim Rukoto a modulated signal applied from the waveguide to the optical waveguide is separated the third optical waveguide group.   In the semiconductor laser according to any one of claims 4 to 7,
  A semiconductor laser characterized in that at least one of the second optical waveguide groups is a curved waveguide including a curved region.

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