JP2008227010A - Light-source apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monolithic integrating type wavelength-tunable light-source apparatus having a simple constitution and excellent productivity. <P>SOLUTION: The light-source apparatus 1 has a first Fabry-Perot resonator (FP) region 2, a semiconductor optical amplifier (SOA) region 3, and a second FP region 4. The first FP region 2, the SOA region 3, and the second FP region 4 are so disposed on a single semiconductor substrate 5 so as to make the second end surface 2b of the first FP region 2 oppose the first end surface 3a of the SOA region 3 via a clearance and so as to make the second end surface 3b of the SOA region 3 oppose the first end surface 4a of the second FP region 4 via a clearance. The free-spectral ranges of the first FP region 2 and the second FP region 4 are different from each other. The light generated in the SOA region 3 is propagated to the first FP region 2 and to the second FP region 4, and the oscillating wavelength of the light-source apparatus 1 is selected by the overlap of the peak of the first FP region 2 with the peak of the second FP region 4. The oscillating wavelength can be varied by varying the refractive indexes of the respective FP regions 2, 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light source device, and more particularly to a wavelength tunable light source device.

  With the explosive demand for broadband multimedia communication services such as the Internet and video distribution, the introduction of high-distance wavelength-division-multiplexed optical fiber communication systems with longer distances, larger capacities, and higher reliability has been added to the trunk and metro lines. The spread of optical fiber access services is rapidly advancing even in the human system. In such an optical fiber communication system, there is a wavelength multiplexing technique for multiplexing and transmitting a plurality of signal lights of different wavelengths from the viewpoint of reducing the installation cost of the optical fiber as a transmission line and increasing the transmission band utilization efficiency per optical fiber. Widely used. As a light source of such a wavelength division multiplexing optical fiber transmission system, a distributed feedback laser diode (DFB-LD) in which a diffraction grating is provided in a resonator of a semiconductor laser diode (LD) or a distributed Bragg reflection is used. Light sources capable of oscillating in a single axis mode, such as a type semiconductor laser diode (DBR-LD; Distributed Bragg Reflector), are required for the number of wavelength channels. In this case, since preparing different light source modules for each wavelength requires enormous costs and inventory, development of a wavelength tunable light source capable of covering a plurality of different wavelength channels with a single light source element is expected.

  Such a wavelength tunable light source includes a plurality of different DFB-LDs and DBR-LDs arranged in an array to multiplex their signal light outputs (array type) (for example, refer to Patent Document 1), and an external gain medium. It is roughly classified into a combination of mirrors (external mirror type) (for example, see Patent Document 2 and Patent Document 3).

  In particular, an external mirror type tunable light source has been developed in recent years because there is a possibility that a single tunable light source module can cover a wide wavelength range. As the wavelength tunable external mirror, for example, one that electrically controls the diffraction wavelength using the change in susceptibility due to the electric field of liquid crystal molecules coated on the surface of the diffraction grating and sealed with a transparent glass electrode (liquid crystal mirror type) (for example, , See Patent Document 4), one that thermally or electrically controls the effective refractive index of a waveguide ring optical resonator (ring optical resonator type), and a waveguide diffraction grating having a plurality of reflection peak wavelengths A group using a group (sampled grating or superstructure grating) (diffraction grating type) (for example, see Patent Document 5) has been proposed.

JP 2004-221267 A JP 2005-150724 A JP 2006-19514 A Japanese Patent Laid-Open No. 2003-133737 JP-A-6-69586

  The array-type tunable light source is excellent in stability of oscillation wavelength, etc., but as the number of wavelength channels to be combined increases, the size of the optical multiplexer increases, the increase in multiplexing loss, dispersion between wavelength channels, array arrangement There are problems such as the enormous heat generation of the selected elements, the influence on the oscillation wavelength and light output due to the heat generation of adjacent elements (mutual thermal interference), and the restriction of element arrangement due to this mutual thermal interference, and the expandability of the number of wavelength channels There is a limit.

  In a liquid crystal mirror type wavelength tunable light source, liquid crystal molecules may be deteriorated at high temperatures, which may affect the optical characteristics and reliability of the reflection wavelength tunable external mirror, and the optical element is mounted in an airtightly sealed module. There are restrictions on the heating process that is indispensable. In a wavelength tunable light source of the ring optical resonator type, there is a concern about damage due to damage or scattering of the dry etching processed surface, and when using the thermo-optic effect for refractive index control, the response speed also becomes a problem. In addition, since the diffraction grating type tunable light source requires advanced diffraction grating design technology and high-definition processing technology, mass production is not easy, and stable control of oscillation wavelength is not easy.

  An object of the present invention is to provide a monolithic integrated wavelength tunable light source device having a simple configuration and excellent mass productivity.

  According to a first aspect of the present invention, a first optical waveguide, a second optical waveguide, and a third optical waveguide are provided, and one end surface of the first optical waveguide and one end surface of the second optical waveguide are interposed via a gap. And the other end face of the second optical waveguide and the one end face of the third optical waveguide are arranged to face each other via a gap, and light is transmitted between the optical waveguides through the opposing end face pairs. The first optical waveguide, the second optical waveguide, and the third optical waveguide are disposed on the same semiconductor substrate so as to propagate, and the second optical waveguide is a semiconductor light having an optical amplification medium and an active mechanism of the amplification medium. The first optical waveguide and the third optical waveguide are formed as Fabry-Perot resonators whose opposite end surfaces are reflecting mirrors, and the free spectral ranges of the first optical waveguide and the third optical waveguide are Light source devices that are different from each other Subjected to.

  According to the preferred form of the first aspect, the optical path length formed between both end faces of the first optical waveguide is different from the optical path length formed between both end faces of the third optical waveguide.

  According to the preferable form of the first viewpoint, both end faces of the second optical waveguide are not perpendicular to the optical waveguide axis of the second optical waveguide.

  According to a preferred form of the first aspect, the angle formed by the optical waveguide axis of the first optical waveguide and the first normal line of one end surface of the second optical waveguide on the projection plane parallel to the semiconductor substrate is The optical waveguide axis of the third optical waveguide is defined in accordance with the angle between the optical waveguide axis of the optical waveguide and the first normal, and the effective refractive index of the second optical waveguide and the gap, and on the projection plane parallel to the semiconductor substrate. And the second normal of the other end face of the second optical waveguide are defined by the angle between the optical waveguide axis of the second optical waveguide and the second normal, and the effective refractive index of the second optical waveguide and the gap. It is prescribed accordingly.

  According to a preferred embodiment of the first aspect, low reflection films are formed on both end faces of the second optical waveguide.

  According to a preferred embodiment of the first aspect, at least one of the first optical waveguide and the third optical waveguide has a refractive index variable mechanism that changes the effective refractive index of the optical waveguide.

  According to the preferred form of the first aspect, the least common multiple of the free spectral range of the first optical waveguide and the free spectral range of the third optical waveguide is larger than the gain wavelength bandwidth of the second optical waveguide.

  According to the preferred embodiment of the first aspect, the free spectral range between the one end surface of the first optical waveguide including the second optical waveguide and the one end surface of the third optical waveguide is the free spectral range of the first optical waveguide. It is between the free spectral range of the third optical waveguide.

  According to a preferred embodiment of the first aspect, the second optical waveguide is a multimode interference optical waveguide having three or more input / output paths, and each input / output path includes a first optical waveguide and a third optical waveguide. And an output optical waveguide for guiding the output light. According to a further preferred embodiment, the light receiving region for monitoring the light output is formed in the input / output path of the second optical waveguide.

  According to the preferable form of the first viewpoint, one end face of the first optical waveguide, both end faces of the second optical waveguide, and one end face of the third optical waveguide are formed by etching.

  First, in the present invention, a waveguide type Fabry-Perot resonator region (FP region) based on a pair of simple mode optical waveguides having a simple structure is used as an external mirror for selecting an oscillation wavelength. . The semiconductor optical amplifier region (SOA region) serving as a gain medium can be monolithically integrated on the same substrate and substantially in series with the pair of waveguide-type Fabry-Perot resonators. Thereby, according to this invention, a simple structure and a small wavelength variable light source device can be obtained.

  Secondly, in the present invention, design / manufacturing techniques of optical elements that have been proven so far can be used for designing and manufacturing the SOA region and the FP region. In addition, the relative positional relationship between the SOA region and the FP region, which affects the light coupling state between each region, can be determined with good reproducibility by epitaxial growth and lithography processes, and movable parts that can cause instability of the resonance state are eliminated. This eliminates the need for optical axis alignment, which has the greatest work load during assembly. As a result, according to the present invention, each process of element design, manufacturing, and module assembly can be simplified and the yield can be improved as compared with the conventional wavelength tunable light source device. Therefore, it is possible to obtain a light source device that is low in cost and excellent in mass productivity.

  Third, the present invention does not require a diffraction grating as means for selecting the oscillation wavelength. Thus, according to the present invention, problems such as waveguide crystallinity degradation and carrier injection inhibition in the diffraction grating forming step can be avoided. Therefore, it is possible to obtain a light source device with high reliability of oscillation characteristics.

  The light source device of the present invention will be described. In FIG. 1, the conceptual diagram which shows the structure of the light source device of this invention is shown. The light source device 1 includes a first Fabry-Perot resonator (FP) region 2 as a first optical waveguide, a semiconductor optical amplifier (SOA) region 3 as a second optical waveguide, and a third optical waveguide. As a second Fabry-Perot resonator region 4. The first FP region 2, the SOA region 3, and the second FP region 4 are arranged such that the second end surface 2b of the first FP region 2 and the first end surface 3a of the SOA region 3 face each other, and the second end surface 3b of the SOA region 3 The second FP region 4 is disposed on the same semiconductor substrate 5 substantially in series (straight) so as to face the first end face 4a.

  The SOA region 3 is preferably linear and has an electrode for injecting carriers into the undoped active layer as an active mechanism for activating the amplifying medium such as current injection means, and confines light in the undoped active layer responsible for light emission. And a so-called buried heterostructure waveguide semiconductor optical amplifier region excellent in current confinement. Accordingly, the SOA region 3 functions as a gain medium (for example, a white light source) that generates a sufficient optical gain to oscillate by compensating for a transmission loss received when light in the oscillation wavelength region reciprocates through the entire light source device 1. .

FIG. 2 shows an enlarged view of a portion where the second end surface 2b of the first FP region 2 and the first end surface 3a of the SOA region 3 face each other in the light source device shown in FIG. Both end surfaces 3a and 3b of the SOA region 3 are inclined (not vertical) with respect to the optical waveguide axis 3c of the SOA region 3 so that light does not resonate between the both end surfaces 3a and 3b. That is, on the projection plane parallel to the surface of the semiconductor substrate 5, the optical waveguide axis 3c and the normal 3d on both end faces 3a and 3b of the SOA region 3 are formed so as to intersect at an angle θ _SOA . The end surfaces 3a and 3b of the SOA region 3 can be formed as a part of the side wall of the wedge-shaped groove by, for example, a dry etching technique.

A dielectric film (low reflection film / antireflection film) (not shown) is preferably formed on both end faces 3a and 3b of the SOA region 3 from the viewpoint of reflection suppression and reliability. The effective end face reflectivity of both end faces 3a and 3b depends on the optical gain in the SOA region 3, but is preferably 0.1% or less. For example, a low reflection film is used, and the optical waveguide axis 3c and the normal line are used. Such a low reflectance can be set by setting the angle θ _SOA formed by 3d to 6 ° to 8 °. The angle theta _SOA at the first end surface 3a and the angle theta _SOA at the second end surface 3b may be different from each other, but preferably is in order to simplify the layout both angles of the same value (absolute value). The orientation of the second end face 3b relative to the orientation of the first end face 3a of the SOA region 3 may be point-symmetric so that the SOA region 3 has a parallelogram shape as shown in FIG. 1, or as shown in FIG. Alternatively, the SOA region 3 may be line-symmetric so as to be trapezoidal.

The first FP region 2 and the second FP region 4 are waveguide-type Fabry-Perot resonator regions, and both end surfaces 2a and 2b of the first FP region 2 and both end surfaces 4a and 4b of the second FP region 4 are reflecting mirrors. Is forming. The first FP region 2 and the second FP region 4 are preferably linear buried heterostructure single-mode optical waveguides. A free spectral range (FSR) Δλ _FP1 in the first FP region ₂ and an FSR Δλ _FP2 in the second _FP region 4 can be set to be different from each other. For example, it is preferable that the optical path length formed between both end faces 2 a and 2 b of the first FP region 2 is different from the optical path length formed between both end faces 4 a and 4 b of the second FP region 4. At least one of the first FP region 2 and the second FP region 4 has a refractive index variable mechanism that can change the effective refractive index of the optical waveguide by current injection, voltage application, temperature adjustment, and the like. In particular, the refractive index change due to current injection or voltage application has a response time as high as nanoseconds, so it is suitable for dynamic selective wavelength switching operation. The refractive index change due to temperature change has a response time of more than milliseconds. Therefore, it is suitable for static correction of the shift of the center wavelength of the reflection spectrum that occurs mainly at the time of manufacturing the device. The shape of the first FP region 2 and the second FP region 4 may be any shape as long as a Fabry-Perot resonance operation can be obtained, but is preferably linear from the viewpoint of design and manufacturing.

  In order to change the reflectance at each end face of the first FP region 2 and the second FP region 4, it is preferable to form a desired dielectric film using partial vapor deposition or chemical etching. In particular, the reflectance product of both end surfaces required for the operation of the first FP region 2 and the second FP region 4 as a wavelength selective reflector (for example, the reflectance of the first end surface 2a and the second end surface 2b in the first FP region 2). When the reflectance product is not obtained, a highly reflective film is formed on the end faces of the first FP region 2 and the second FP region 4.

  Further, the first FP region 2 and the second FP region 4 may have a mechanism for generating optical gain in order to compensate for optical loss.

In the first FP region 2 and the SOA region 3, and in the SOA region 3 and the second FP region 4, light emitted from one end face propagates to the other through a gap between the optical waveguides through the opposite end faces (a pair). Are arranged to be. The first FP region 2 and the second FP region 4 are disposed via the end faces 3 a and 3 b of the SOA region 3 and the gap 6, respectively. For example, as shown in FIG. 2, when attention is paid to the relationship between the first FP region 2 and the SOA region 3, the light of the first FP region 2 indicating the normal direction of the second end surface 2b on the projection plane parallel to the semiconductor substrate surface. The first FP region 2 and the SOA region 3 are arranged so that the wave axis 2c and the normal 3d of the first end face 3a of the SOA region 3 intersect at an angle θ _gap . Angle theta _GAP, the effective refractive index of the SOA region 3 _{n SOA,} from Snell's law when the effective refractive index _{n GAP} of the gap 6, the number 1 is obtained. Then, Equation 2 is derived from Equation 1.

  The optical path length in the gap 6 between the first FP region 2 and the second FP region 4 and the SOA region 3 is preferably 5 μm or less. If the optical path length of the gap 6 is long, the light emitted from each optical waveguide is not confined in the gap 6 and is attenuated exponentially, and the effective optical coupling efficiency between the optical waveguides is reduced. Because it will end up.

  Next, a detailed configuration of the light source device 1 will be described. FIG. 4 shows a schematic plan view of the light source device 1. FIG. 5 shows a schematic cross-sectional view (hatching omitted) taken along the line VV in FIG. 4, and FIG. 6 shows a schematic cross-sectional view (hatched omitted) taken along the line VI-VI in FIG. In FIG. 4, the optical waveguides (undoped active layer 24 and undoped core layer 44) are indicated by dotted lines.

As described with reference to FIGS. 1 and 2, the first FP region 2, the SOA region 3, and the second FP region 4 are arranged substantially in series with their end faces facing each other. A gap 6 between the first FP region 2 and the SOA region 3 and a gap 7 between the SOA region 3 and the second FP region 4 are regions etched from the uppermost surface to the lower cladding layers 22 and 42. That is, the inner wall surface of the gap 7 becomes the second end surface 2b of the first FP region 2 and the first end surface 3a of the SOA region 3 so that the inner wall surface of the gap 7 becomes the second end surface 3b and the second FP region of the SOA region 3. Etching treatment of a wedge shape or a triangle shape is performed so that the first end surface 4a of the fourth shape is formed. For example, it is preferable to perform the etching process so that θ _SOA is in the range of 6 ° to 8 ° and θ _gap is in the range of 19 ° to 22 °.

  Since a plurality of current injection or voltage application regions are formed on the semiconductor substrate 5, the first FP region 2, the SOA region 3, and the second FP region 4 must be electrically insulated (isolated) from each other. . Therefore, in the first FP region 2 and the second FP region 4, insulating grooves 54 are formed by etching treatment on both sides of the undoped core layer 44 along the waveguide, and in the SOA region 3, the undoped active layer is formed along the waveguide. Insulating grooves 34 are formed on both sides of the layer 24 by etching to ensure insulation between the regions. The insulating grooves 34 and 54 can be formed as grooves having a width of 5 μm to 10 μm, for example. In the form shown in FIG. 4, the insulating groove 54, the gap 6, the insulating groove 34, and the gap 7 are formed so as to communicate with each other.

  Both end surfaces of the light source device 1 (the first end surface 2a of the first FP region 2 and the second end surface 4b of the second FP region 4) are preferably formed by cleavage. High-reflection films (not shown) are provided on both end surfaces 2a and 2b of the first FP region 2 and both end surfaces 4a and 4b of the second FP region 4 so as to obtain desired characteristics, and both end surfaces 3a and 3b of the SOA region 3 are obtained. A low reflection film (not shown) is appropriately formed.

  The end portions of the upper electrodes 32 and 52 are formed, for example, inside 5 μm to 10 μm from each end surface of each region.

  As shown in FIG. 5, the SOA region 3 is formed on the semiconductor substrate 5 with a lower cladding layer 22, an undoped lower optical confinement layer 23, an undoped active layer 24, an undoped upper confinement layer 25, an upper cladding layer 26, and a contact layer 27. These layers are embedded on both sides by a buried layer 28, a carrier trap layer 29 and a buried cladding layer 30. In the buried layer 28, the carrier trap layer 29, and the buried cladding layer 30, insulating grooves 34 are formed on both sides along the undoped active layer 24 and the like. Further, an upper electrode 32 and a lower electrode 33 for current injection, and an insulating film 31 are formed.

  As shown in FIG. 6, the FP regions 2 and 4 have the same configuration as that of the SOA region 3, and on the semiconductor substrate 5, there are a lower cladding layer 42, an undoped lower optical confinement layer 43, an undoped core layer 44, and an undoped upper portion. The confinement layer 45, the upper clad layer 46, and the contact layer 47 have a buried layer 48, a carrier trap layer 49, and a buried clad layer 50 on both sides. In the buried layer 48, the carrier trap layer 49, and the buried cladding layer 50, insulating grooves 54 are formed on both sides along the undoped core layer 44 and the like. Further, an upper electrode 52 and a lower electrode 53 for changing the refractive index, and an insulating film 51 are formed.

  Next, a method for manufacturing the light source device 1 will be described. FIG. 7 shows a manufacturing process diagram based on a schematic plan view, and FIG. 8 shows a manufacturing process diagram of the SOA region 3 (hatching omitted) based on a schematic cross-sectional view taken along the line VV of FIG. In FIG. 7, the positions where the respective regions such as the SOA region 3 are formed are indicated by dotted lines.

  First, in the first crystal growth, stacked structures 22 to 27 of the SOA region 3 were formed (FIG. 7A). That is, the lower clad layer 22, the undoped lower light confinement layer 23, the undoped active light confinement layer 24, the undoped upper light confinement layer 25, the upper clad layer 26, and the hetero barrier relaxation layer (thin film thickness is thin) on the semiconductor substrate 5 in order from the bottom. Therefore, the contact layer 27 is continuously grown using metal organic chemical vapor deposition (MOVPE) or the like.

  Next, an etching stopper film 35 is formed on the contact layer 27 to protect it from etching in order to leave the SOA region 3 (FIGS. 7B and 8A).

  Next, the stacked structures 22 to 27 formed outside the SOA region 3 are removed by etching (FIG. 7C).

  Next, in the second crystal growth, the stacked structures 42 to 47 of the first FP region 2 and the second FP region 4 are formed around the SOA region 3 (FIG. 7D). That is, in the same manner as the first crystal growth, on the semiconductor substrate 5 around the SOA region 3, the lower cladding layer 42, the undoped lower optical confinement layer 43, the undoped core layer 44, and the undoped upper optical confinement layer are sequentially formed from the bottom. 45, the upper clad layer 46, the hetero barrier relaxation layer (not shown because the film thickness is thin), and the contact layer 47 are continuously grown using metal organic chemical vapor deposition (MOVPE) or the like.

  Next, in order to leave the laminated structure that becomes the waveguide of the first FP region 2, the SOA region 3, and the second FP region 4, an etching stopper film 36 that protects from etching is formed on the contact layers 27 and 47 (FIG. 7 ( E)).

  Next, the stacked structures 22 to 27 and 42 to 47 formed in regions other than the region to be the waveguide are removed by etching (FIGS. 7F and 8B).

  Next, in the third crystal growth, a buried layer is formed around the region to be the waveguide (FIGS. 7G and 8C). That is, the buried layers 28 and 48, the carrier trap layers 29 and 49, and the buried cladding layers 30 and 50 were continuously grown on the semiconductor substrate 5.

  Next, an etching stopper film 37 is formed on the contact layers 27 and 47 and the buried cladding layers 30 and 50, and the gaps 6 and 7 (end surfaces of the respective regions 2, 3, and 4) and the insulating grooves 34 and 54 are etched. It forms (FIG.8 (d)). FIG. 8H shows a state after the etching stopper film 37 is removed.

  Next, upper electrodes 32 and 52, lower electrodes 33 and 53, and insulating films 31 and 51 for applying current or applying voltage to the optical waveguide are formed (FIG. 8E).

  Finally, if necessary, low reflection films (not shown) are formed on both end surfaces 3a and 3b of the SOA region 3, and high on both end surfaces 2a, 2b, 4a and 4b of the first FP region 2 and the second FP region 4. A reflective film (not shown) is formed.

  Next, operation | movement of the light source device 1 of this invention is demonstrated. First, current is injected into the SOA region 3, and light in the SOA region 3 is reflected on the second end surface 2 b of the first FP region 2 and the first end surface 4 a of the second FP region 4 as reflecting mirrors. Amplified by reciprocating between 2b and the first end face 4a of the second FP region 4. At this time, part of the light reflected by the second end surface 2 b of the first FP region 2 and the first end surface 4 a of the second FP region 4 is propagated into the first FP region 2 and the second FP region 4.

Here, the first FP region 2 and the second FP region 4 are reflectors having wavelength selectivity in which a peak periodically appears at a constant optical wavelength interval (FSR) Δλ _FP . In FIG. 9, the conceptual diagram of the spectrum characteristic in the light source device 1 of this invention is shown. 9A is a conceptual diagram of a spectral characteristic selected by the first FP region 2, FIG. 9B is a conceptual diagram of a spectral characteristic selected by the second FP region 4, and FIG. 9C is a diagram of FIG. 9 (a) and FIG. 9 (b) are conceptual diagrams of spectral characteristics of overlapping portions, and FIG. 9 (d) are conceptual diagrams of spectral characteristics of gain wavelengths in the SOA region 3. If the FSRΔλ _FP1 of the first _FP region 2 and the FSRΔλ _FP2 of the second _FP region 4 are different from each other, the reflection peak overlaps for each FSRΔλ _{FP L which} is the least common multiple of both FSRΔλ _FP1 and Δλ _FP2 , and the oscillation wavelength λ ₀ is selected. The

As shown in FIG. 9C, even if a plurality of overlapping peaks occur, multimode oscillation can be avoided by a combination with the gain wavelength band Δλ _Gain in the SOA region 3. That is, as shown in FIG. 9 (d), as well as to the oscillation wavelength lambda ₀ is included in the gain wavelength band [Delta] [lambda] _Gain, by setting as conditions FSRΔλ _L> gain wavelength band [Delta] [lambda] _Gain is satisfied, Single mode oscillation can be ensured.

Furthermore, by narrowing the bandwidth using the resonance between the second end face 2b of the first FP region 2 and the first end face 4a of the second FP region 4, that is, the resonance in the SOA region 3 and the gaps 6 and 7 on both sides thereof, The accuracy of the selected wavelength can be further increased. For example, the FSRΔλ _FP1 of the first _FP region 2 is 197.5 GHz, the FSRΔλ _SOA between the two end faces 2b and 4a including the SOA region 3 is 200 GHz, and the FSRΔλ _FP2 of the second _FP region 4 is 202.5 GHz. Can improve the accuracy.

When the light having the oscillation wavelength λ ₀ reaches a sufficient gain, the light source device 1 starts single axis mode oscillation. If the effective refractive indexes of the first FP region 2 and the second FP region 4 are changed, the overlapping position of the reflection peaks can be changed over a wide wavelength range, and the light source device 1 can be tunable in wavelength capable of single axis mode oscillation. Functions as a light source. In this way, the principle of widening the wavelength selection range by slightly shifting the reflection spectrum of a pair of wavelength selective reflectors having different FSRs is based on the relationship between the caliper main scale and the vernier scale. By the way, it is called the vernier principle (or vernier effect).

The difference between the FSRΔλ _FP1 in the first _FP region 2 and the FSRΔλ _FP2 in the second _FP region 4 is determined by how many wavelength channels are oscillated. The number wavelength channels, and the 1FP region 2 FSRderutaramuda _FP1 an average of FSRderutaramuda _FP2 of the 2FP region 4, divided by the difference between the _{FSR {(Δλ FP1 + Δλ FP2} ) / 2} / (Δλ FP1 -Δλ FP2 ) Can be almost determined. For example, if Δλ _FP1 = 202.5 GHz and Δλ _FP2 = 197.5 GHz, about 40 wavelength channels are oscillated.

  According to the light source device of the present invention, the wavelength can be changed with a simple and small configuration in which the SOA region and the pair of FP regions are monolithically integrated. Even in the manufacture of light source devices, it is not necessary to form complicated diffraction gratings, and the relative positional relationship between the SOA area and the FP area can be determined by a high-precision lithography process, so that optical axis alignment and fixing operations are not required. Thus, the manufacturing cost can be suppressed. Further, it can be manufactured by basically the same process as a Fabry-Perot type semiconductor laser diode (FP-LD) which has already been put into practical use.

  Next, a light source device according to a second embodiment of the invention will be described. FIG. 10 is a schematic plan view showing a configuration example of the light source device according to the second embodiment of the present invention. In FIG. 10, the optical waveguide and the active layer are shown by dotted lines. In the second embodiment, the SOA region 63 having the structure of a multimode interference type optical multiplexer / demultiplexer is used.

  In the light source device 61, the first FP region 62 and the second FP region 64 are formed on both sides of the SOA region 63 as in the first embodiment. Here, the SOA region 63 is configured as an active MMI having a total of four input / output paths as shown in FIG. The first FP region 62 and the second FP region 64 are disposed opposite to the input / output path on the diagonal line of the SOA region 63. A gap 72 is formed between the first FP region 62 and the SOA region 63 by an etching process, and the first end surface is inclined with respect to the second end surface 62b of the first FP region 62 and the optical waveguide axis of the SOA region 63. 63a is formed. Similarly, a gap 73 is formed between the second FP region 64 and the SOA region 63 by etching, and is inclined with respect to the first end face 64 a of the second FP region 64 and the optical waveguide axis of the SOA region 63. A second end face 63b is formed.

  The first end surface 62a of the first FP region 62 facing the outside of the light source device 61 and the second end surface 62b of the second FP region 64 are formed by an etching region 70 formed by etching in the same manner as the gaps 72 and 73. Yes.

  The light source device 61 further includes a light receiving area 65, and the light receiving area 65 is disposed to face one input / output path. The light receiving region 65 can monitor the light output in the oscillation state by receiving light with a reverse bias applied and measuring the photocurrent. The light receiving region 65 has the same structure as the schematic sectional view of the SOA region shown in FIG.

  In the remaining input / output paths, an output optical waveguide core layer 66 (a laminated structure similar to the FP region) for extracting light extends from the SOA region 63 to the end of the light source device 61.

  Preferably, the end surface of the light source device 61 (the end surface of the light receiving region 65 and the output optical waveguide 66), the both end surfaces 62a and 62b of the first FP region 62, and the both end surfaces 64a and 64b of the second FP region 64 are highly reflective films (non-reflective films). A low reflection film (not shown) is formed on both end faces 63a and 63b of the SOA region 63.

  The four input / output paths can be formed after crystal growth using, for example, inductively coupled plasma reactive ion etching technology.

Examples of the light source device according to the first embodiment of the present invention will be described. In this example, a light source device as shown in FIGS. 4 to 6 was produced by the steps shown in FIGS. First, as an SOA region, an n-InP lower clad layer, an undoped InGaAsP lower optical confinement layer (wavelength composition 1250 nm), an undoped InGaAsP / InGaAsP strained multiple quantum well active layer (transition wavelength 1560 nm) in order from the bottom on an n-Inp semiconductor substrate. ), An undoped InGaAsP upper optical confinement layer (wavelength composition 1250 nm), a p-InP upper cladding layer, a p-InGaAsP heterobarrier relaxation layer (wavelength composition 1400 nm), and a p ⁺ -InGaAs contact layer are formed by metalorganic vapor phase epitaxy ( MOVPE). The laminated structure of the waveguide was processed to a width of 1.3 μm using an inductively coupled plasma reactive ion etching technique using the SiN etching stop film as a mask.

  Next, a Ru-doped semi-insulating InP layer, an n-Inp hole trap layer, and a p-InP buried cladding layer were formed as buried layers on both side surfaces of the laminated structure of the waveguide. Next, after forming the SiN film as an etching stop film, the insulating grooves on both side surfaces of the buried layer and the gap whose end face is inclined with respect to the optical waveguide axis are formed in the two-frequency RF excitation inductively coupled plasma type reactive ion. A buried heterostructure single-mode optical waveguide was formed by etching. The formation of the buried layer and the formation of the insulating groove and the gap were performed simultaneously with the production of the first FP region and the second FP region. Next, a Ti—Pt—Au electrode and an insulating film for injecting carriers into the strained multiple quantum well active layer were formed. Moreover, low reflection films were formed on both end faces of the SOA region.

As the FP region, a pair of waveguide type Fabry-Perot resonator regions were formed. An n-InP lower clad layer, an undoped InGaAsP lower optical confinement layer (wavelength composition 1300 nm), an undoped InGaAsP / InGaAsP multiple quantum core layer (transition wavelength 1400 nm), and an undoped InGaAsP upper optical confinement layer on an n-InP semiconductor substrate in order from the bottom (Wavelength composition 1300 nm), p-InP upper cladding layer, p-InGaAsP hetero barrier relaxation layer (wavelength composition 1400 nm), and p ⁺ -InGaAs contact layer are grown continuously using metal organic vapor phase epitaxy (MOVPE). I let you. Next, as described above, a buried layer, an insulating groove and a gap were formed simultaneously with the fabrication of the SOA region. Next, a Ti—Pt—Au electrode and an insulating film for injecting carriers into the multiple quantum well core layer to control the effective refractive index were formed.

  The length of the SOA region in the optical waveguide direction was 400 μm, and the effective refractive index for signal light with a wavelength of 1530 to 1570 nm was approximately 3.45 and constant. The normals of both end faces of the SOA region were parallel to the n-InP semiconductor substrate and inclined by 7 ° with respect to the signal light propagation axis, and the effective residual end face reflectivity of both end faces was 0.1% or less.

The pair of FP regions are arranged such that each signal light propagation axis forms an angle θ _gap of about 22 ° with respect to the end surface of the SOA region, with a gap of 3 μm in optical path length from the SOA region. . The effective refractive index at the time of no carrier injection with respect to signal light having a wavelength of 1530 to 1570 nm in the FP region is almost constant at 3.35, and each FSR has a longer element length of 50 GHz and a shorter one of 51 GHz.

  When a forward bias current was passed through the SOA region, single axis mode oscillation occurred at 25 ° C. with a threshold current of 20 mA, an oscillation wavelength of 1550 nm, and a side mode suppression ratio of 50 dB or more. In addition, by controlling the current injected into each FP region optimally in the range of 0 mA to 15 mA, wideband wavelength variable operation over a wide wavelength range of 1530 nm to 1570 nm was realized. Furthermore, the time required for switching the oscillation wavelength was about 10 nsec or less, and a sufficient high speed without any practical problem was confirmed.

  Examples of the light source device according to the second embodiment of the present invention will be described. In this example, a light source device as shown in FIG. 10 was produced. The laminated structure of the waveguide and the buried layer in the SOA region, the first FP region, and the second FP region is the same as that in the first embodiment.

  In the SOA region, after the first crystal growth, by using the inductively coupled plasma reactive ion etching technique, a total of four single-mode optical waveguides (width 1.3 μm) having a width of 12 μm and a length of 239 μm are formed. It was processed into the shape of a connected multimode interference (MMI) type optical multiplexer / demultiplexer.

  The effective refractive index with respect to signal light having a wavelength of 1530 to 1570 nm of the total of four single mode optical waveguides was approximately 3.35 and constant. The normals of both end faces facing the FP region were parallel to the n-InP substrate and inclined by 7 ° with respect to the signal light propagation axis. The effective residual end face reflectance including the low reflection film applied to both the oblique end faces was suppressed to 0.1% or less.

A pair of waveguide-type FP optical resonator regions (FP regions) are arranged so that one end surfaces thereof are opposed to the respective oblique end surfaces of the SOA region with a gap of 3 μm in length, and each of the FP region and the SOA region. The angle θ _gap formed by the signal light propagation axis is set to about 22 °.

  In addition, a light receiving region having the same structure as the SOA region of Example 1 was formed on one waveguide.

  When a forward bias current was passed through the SOA region, single-axis mode oscillation occurred at 25 ° C. with a threshold current of 40 mA, an oscillation wavelength of 1550 nm, and a side mode suppression ratio of 50 dB or more. In addition, a broadband wavelength variable operation over a wide wavelength range of 1530 nm to 1570 nm was realized by optimally controlling the current injected into each waveguide type FP optical resonator region in the range of 0 mA to 15 mA. Furthermore, the time required for switching the oscillation wavelength was about 10 nsec or less, and a sufficient high speed without any practical problem was confirmed. When a reverse bias voltage was applied to the light receiving region, a photocurrent proportional to the oscillation light output was taken out.

  Although the light source device of the present invention has been described using the above embodiment and examples, the present invention is not limited to the above embodiment and examples, and may include various modifications, changes, and improvements within the scope of the present invention. Needless to say, it can be done.

The conceptual diagram which shows the structural example of the light source device which concerns on 1st Embodiment of this invention. FIG. 2 is an enlarged view of a part of the light source device shown in FIG. 1. The conceptual diagram which shows another structural example of the light source device which concerns on 1st Embodiment of this invention. 1 is a schematic plan view of a light source device according to a first embodiment of the present invention. The schematic sectional drawing in the VV line of FIG. The schematic sectional drawing in the VI-VI line of FIG. The schematic plan view for demonstrating the manufacturing method of the light source device which concerns on 1st Embodiment of this invention. The schematic sectional drawing for demonstrating the manufacturing method of the SOA area | region in the light source device which concerns on 1st Embodiment of this invention. The conceptual diagram of the spectrum characteristic in the light source device of this invention. The schematic plan view of the light source device which concerns on 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source device 2 1st FP area | region 2a 1st end surface 2b 2nd end surface 2c Optical waveguide axis | shaft 3 SOA area | region 3a 1st end surface 3b 2nd end surface 3c Optical waveguide axis 3d Normal line 4 2nd FP area | region 4a 1st end surface 4b 2nd end surface 5 Semiconductor substrate 6 Gap 7 Gap (etching area)
22 lower cladding layer 23 undoped lower optical confinement layer 24 undoped active layer 25 undoped upper optical confinement layer 26 upper cladding layer 27 contact layer 28 buried layer 29 carrier trapping layer 30 buried cladding layer 31 insulating film 32 upper electrode 33 lower electrode 34 insulating groove 35 etching blocking film 36 etching blocking film 37 etching blocking film 42 lower cladding layer 43 undoped lower optical confinement layer 44 undoped core layer 45 undoped upper optical confinement layer 46 upper cladding layer 47 contact layer 48 buried layer 49 carrier trapping layer 50 buried cladding layer 51 Insulating film 52 Upper electrode 53 Lower electrode 54 Insulating groove 61 Light source device 62 First FP region 62a First end surface 62b Second end surface 63 SOA region 63a First end surface 63b Second end surface 4 The 2FP region 64a first end surface 64b second end surface 65 the light receiving region 66 the output optical waveguide core layer 67 upper electrode 68 upper electrode 69 upper electrode 70 etched region 71 insulating groove 72 gap (etched region)
73 Gap (etching area)

Claims (11)

A first optical waveguide, a second optical waveguide, and a third optical waveguide;
One end face of the first optical waveguide and one end face of the second optical waveguide are arranged to face each other through a gap, and the other end face of the second optical waveguide and one of the third optical waveguides The end surface is arranged opposite to the gap, and
The first optical waveguide, the second optical waveguide, and the third optical waveguide are arranged on the same semiconductor substrate so that light propagates between the optical waveguides through a pair of opposing end faces,
The second optical waveguide is formed as a semiconductor optical amplifier having an optical amplification medium and an activation mechanism of the amplification medium,
The first optical waveguide and the third optical waveguide are formed as Fabry-Perot resonators in which both end surfaces are reflecting mirrors,
The light source device, wherein free spectral ranges of the first optical waveguide and the third optical waveguide are different from each other.   2. The light source device according to claim 1, wherein an optical path length formed between both end faces of the first optical waveguide is different from an optical path length formed between both end faces of the third optical waveguide.   3. The light source device according to claim 1, wherein both end faces of the second optical waveguide are not perpendicular to an optical waveguide axis of the second optical waveguide. In the projection plane parallel to the semiconductor substrate, the angle formed by the optical waveguide axis of the first optical waveguide and the first normal line of the one end surface of the second optical waveguide is the optical waveguide axis of the second optical waveguide. And the angle between the first normal line and the effective refractive index of the second optical waveguide and the gap,
On the projection plane parallel to the semiconductor substrate, the angle formed by the optical waveguide axis of the third optical waveguide and the second normal line of the other end surface of the second optical waveguide is the optical waveguide axis of the second optical waveguide. The light source according to any one of claims 1 to 3, wherein the light source is defined according to an angle formed by the second normal line and an effective refractive index of the second optical waveguide and the gap. apparatus.   The light source device according to claim 1, wherein low reflection films are formed on both end faces of the second optical waveguide.   6. The refractive index variable mechanism according to claim 1, wherein at least one of the first optical waveguide and the third optical waveguide includes a refractive index variable mechanism that changes an effective refractive index of the optical waveguide. Light source device.   7. The least common multiple of the free spectral range of the first optical waveguide and the free spectral range of the third optical waveguide is larger than the gain wavelength bandwidth of the second optical waveguide. The light source device according to item.   The free spectral range between the one end face of the first optical waveguide including the second optical waveguide and the one end face of the third optical waveguide is the free spectral range of the first optical waveguide and the third optical waveguide. The light source device according to claim 1, wherein the light source device is in a free spectral range. The second optical waveguide is a multimode interference optical waveguide having three or more input / output paths,
9. The input / output path is formed with the first optical waveguide, the third optical waveguide, and an output optical waveguide for guiding output light. The light source device according to item.   The light source device according to claim 9, wherein a light receiving region for monitoring light output is formed in the input / output path of the second optical waveguide.   11. The one end face of the first optical waveguide, the both end faces of the second optical waveguide, and the one end face of the third optical waveguide are formed by etching. The light source device according to any one of the above.

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