Patent ID: 12218480

DETAILED DESCRIPTION

FIG.1shows a plan view of a semiconductor optical amplifier integrated laser.FIG.2shows a schematic cross-sectional view taken along the line A-A′ ofFIG.1.FIG.3shows a schematic cross-sectional view taken along the line B-B′ inFIG.1, andFIG.4shows a schematic cross-sectional view taken along the line C-C′ inFIG.1.

Referring toFIG.1, a semiconductor optical amplifier integrated laser100includes a semiconductor laser oscillator portion20that oscillates light having a predetermined wavelength, and a semiconductor optical amplifier portion10that amplifies the laser-oscillated light. In the present implementation, the semiconductor laser oscillator portion20is a DFB laser diode (DFB-LD).

The semiconductor laser oscillator portion20and the semiconductor optical amplifier portion10have one common p-i-n structure. “One common p-i-n structure” means a p-i-n structure made of the same material and formed by the same process. Since the semiconductor laser oscillator portion20and the semiconductor optical amplifier portion10have one common structure, the gain band of the semiconductor laser oscillator portion20and the gain band of the semiconductor optical amplifier portion10are substantially the same. Here, the gain band indicates a wavelength range of the gain spectrum. The semiconductor optical amplifier integrated laser100also includes a low reflection end surface coating film11provided on the laser emission surface and a high reflection end surface coating film12on the surface opposite to the laser emission surface. In the present implementation, the oscillation wavelength of the semiconductor laser oscillator portion20is 1.3 μm band, but the oscillation wavelength may be 1.55 μm band.

As shown inFIGS.3and4, the semiconductor optical amplifier integrated laser100includes a mesa unit1and a buried layer27that embeds the mesa unit1from both sides. The semiconductor optical amplifier integrated laser100further includes an insulating film26that covers a part of the buried layer27, and an electrode13that covers a part of the mesa unit1and the insulating film26. The solid line that defines the mesa unit1represents the contour of the mesa unit1.

Referring toFIG.2, the semiconductor optical amplifier integrated laser100has a first conductivity type substrate21and a p-i-n structure provided on the first conductivity type substrate21. In the present implementation, the p-i-n structure includes a first conductivity type SCH layer22, an active layer23, a second conductivity type SCH layer24, and a second conductivity type cladding layer25, but the present disclosure is not limited thereto. In this implementation, the first conductivity type is n-type, the second conductivity type is p-type, and the first conductivity type substrate21is n-InP. The first conductivity type SCH layer22is n-InGaAsP, the active layer23is a multiple quantum well made of InGaAsP or InGaAlAs, the second conductivity type SCH layer24is p-InGaAsP, and the second conductivity type cladding layer25is p-InP. Further, the second conductivity type dopant is Zn. Further, the composition of InGaAsP or InGaAlAs in the active layer23is adjusted to emit light at 1.3 μm, but when emitting at another wavelength, it is adjusted to emit at that wavelength.

The semiconductor optical amplifier integrated laser100further includes a first conductivity type electrode14provided on the lower surface of the first conductivity type substrate21and the second conductivity type electrode13provided on the p-i-n structure. The electrodes13and14are used to inject a current from an external power source (not shown) into the semiconductor optical amplifier integrated laser100(semiconductor laser oscillator portion20and semiconductor optical amplifier portion10). Each of the electrodes13and14is composed of one member. That is, the semiconductor optical amplifier portion10and the semiconductor laser oscillator portion20are energized by a common electrode. Although the substrate21and the SCH layer22are n-type and the SCH layer24and the cladding layer25are p-type in the present implementation, the p-type and the n-type may be opposite.

The semiconductor optical amplifier integrated laser100further includes one common functional layer2in the p-type cladding layer25of the p-i-n structure. The functional layer2is separated from the active layer23of the p-i-n structure. The functional layer2is constituted of a first portion4and a second portion3. The functional layer2has a different composition than that of the p-type cladding layer25. Here, the functional layer2is composed of InGaAsP. As will be described later, the functional layer2is composed of a film formation region and a non-film formation region, the film formation region is InGaAsP, and the non-film formation region is the same p-InP as the p-type cladding layer25.

As shown inFIGS.1and2, the first portion4and the second portion3include openings. In other words, the first portion4and the second portion3include, in a plan view, a first region where a layer is formed (hereinafter, referred to as a “film formation region”) and a second region where a layer is not formed (hereinafter, referred to as “non-film formation region”). In the first portion4, the film formation region and the non-film formation region are periodically provided to reflect light having a specific wavelength within the gain band of the p-i-n structure (first grating structure). With the present grating structure, the semiconductor laser oscillator portion20oscillates laser light having a single oscillation wavelength (DFB wavelength). In general, a grating structure that oscillates at a wavelength near the peak of the gain band is provided. In the present implementation, the first portion4is a floating type grating, has a grating period of 200 nm to oscillate at 1.3 μm, and has a duty ratio of 50%. That is, in a plan view of the first portion4, the area ratio of the film formation region to the non-film formation region is 1:1.

On the other hand, the second portion3is provided with an opening so as not to reflect light having a wavelength within the gain band of the p-i-n structure (to transmit light in the gain band). That is, in the second portion3, the film formation region and the non-film formation region are provided so as not to reflect (to transmit) light having a wavelength within the gain band of the p-i-n structure (second grating structure). In the first portion4and the second portion3, it is preferable that the ratio of the area of the film formation region to the area of the non-film formation region (aperture ratio) is substantially the same. That is, in a plan view of the functional layer2, it is preferable that the ratio of the total area of the film formation regions to the total area of the non-film formation regions in the first portion4, and the ratio of the total area of the film formation regions to the total area of the non-film formation regions in the second portion3are substantially the same. In the present implementation, in a plan view of the functional layer2, the difference between the ratio of the total area of the film formation regions to the total area of the non-film formation regions in the first portion4, and the ratio of the total area of the film formation regions and the ratio of the total area of the non-film-forming regions in the second portion3is within 10%. Although the structure of the second portion3is referred to as a grating here for convenience, it does not reflect light having a wavelength within the gain band as described above.

In the present implementation, the second portion3includes the film formation region and the non-film formation region periodically but is configured not to reflect light having a wavelength within the gain band of the p-i-n structure of the semiconductor optical amplifier integrated laser100. In addition, the second portion3has a structure (grating structure) in which the film formation regions and the non-film formation regions are alternately arranged at the same period, but the film formation regions and the non-film formation regions of the second portion3may not be formed at the same period (seeFIG.5). If the second portion3has a structure in which the film formation regions and the non-film formation regions are alternately arranged at the same period, the duty ratio of the first portion4may be 1.1 times or more or 0.9 times or less of the duty ratio of the second portion3, in consideration of the wavelength range of the gain spectrum of InGaAsP or InGaAlAs forming the active layer23.

The inside of the semiconductor laser oscillator portion20including the first portion4that functions as a grating may be, for example, a uniform grating type DFB-LD that forms a grating of the same period over the entire DFB-LD, a λ/4 shift DFB-LD in which a phase shift of a grating phase π is introduced in the middle of the grating, corrugation pitch modulated (CPM)-DFB-LD in which a phase shift equivalent to λ/4 is realized by slightly changing the grating period, a multi-phase shift DFB-LD in which a λ/4 shift is realized by a plurality of phase shifts, or the like.

When the second portion3has a periodicity, a period that does not reflect the light of the DFB wavelength may be required. In addition, in order to suppress DFB mode oscillation at an unintended wavelength, the second portion3preferably has a period and a diffractive structure with no reflection over the entire wavelength band in which the active layer23has a gain.

Referring toFIG.3, the mesa unit1includes the first conductivity type substrate21and the p-i-n structure provided on the first conductivity type substrate21. In the present implementation, the p-i-n structure includes the first conductivity type SCH layer22, the active layer23, the second conductivity type SCH layer24, and the second conductivity type cladding layer25, but the present disclosure is not limited thereto. The mesa unit1further includes the first portion4formed in a second conductivity type semiconductor layer of the p-i-n structure. The first portion4functions as a grating that reflects light of the oscillation wavelength of the active layer23.

Referring toFIG.4, the mesa unit1includes the first conductivity type substrate21and the p-i-n structure provided on the first conductivity type substrate21. In the present implementation, the p-i-n structure includes the first conductivity type SCH layer22, the active layer23, the second conductivity type SCH layer24, and the second conductivity type cladding layer25, but the present disclosure is not limited thereto. The mesa unit1further includes the second portion3formed in the p-type semiconductor layer of the p-i-n structure. The second portion3does not reflect (transmits) light having a wavelength within the gain band of the active layer23.

FIG.5shows an example of a plan view of a semiconductor optical amplifier integrated laser according to a modification. The modification shown inFIG.5is the same as the implementation shown inFIGS.1to4except for the second portion3. More specifically, inFIG.5, the second portion3does not form a structure in which film formation regions and non-film formation regions are alternately arranged at the same period. That is, the film formation regions and the non-film formation regions in the second portion3are not provided periodically. Further, in this modification, the areas of the film formation region and the non-film formation region may be non-uniform. However, the difference between the aperture ratio of the second portion3and the aperture ratio of the first portion4is within 10% in a plan view.

As described above, the semiconductor optical amplifier portion10and the semiconductor laser oscillator portion20have one common structure except for the functional layer2. Therefore, the semiconductor optical amplifier portion10and the semiconductor laser oscillator portion20have substantially the same gain band. Further, since the electrodes13and14are each made of one member, the same voltage is applied to the semiconductor optical amplifier portion10and the semiconductor laser oscillator portion20. Carriers are injected into the semiconductor optical amplifier portion10and the semiconductor laser oscillator portion20by applying a voltage to the semiconductor optical amplifier portion10and the semiconductor laser oscillator portion20. After carrier injection, the semiconductor optical amplifier portion10and the semiconductor laser oscillator portion20cause radiative recombination.

The semiconductor optical amplifier integrated laser of the present application includes the first portion4functioning as a grating layer in the semiconductor laser oscillator portion20, and the second portion3in the semiconductor optical amplifier portion10. Since the first portion4has a high reflectance for a specific wavelength within the gain band, the semiconductor laser oscillator portion20oscillates light of a single wavelength. On the other hand, the second portion3does not reflect light having a wavelength within the gain band (does not cause Bragg reflection) and thus does not return light having a wavelength within the gain band including the DFB light. Therefore, the semiconductor optical amplifier portion10amplifies the laser light (DFB light) output from the semiconductor laser oscillator portion20.

Since the aperture ratios of the first portion4and the second portion3are substantially the same, the diffusion profile of the second conductivity type dopant in the semiconductor laser oscillator portion and the semiconductor optical amplifier portion is substantially the same within the range of manufacturing variations. Therefore, the diffusion profile of the second conductivity type dopant can be optimized for both the semiconductor laser oscillator portion20and the semiconductor optical amplifier portion10at the same time. As a result, improvement of the characteristics of the semiconductor optical amplifier integrated laser of the present application is realized.

Further, since the aperture ratios of the first portion4and the second portion3are substantially the same, the density of the current injected into the active layer23of each of the semiconductor laser oscillator portion20and the semiconductor optical amplifier portion10is substantially the same within the range of manufacturing variations. Therefore, the difference in current density between the semiconductor laser oscillator portion20and the semiconductor optical amplifier portion10can be reduced as compared with the semiconductor optical amplifier integrated laser in which the semiconductor optical amplifier portion10does not include the second portion. As a result, the operational reliability of the semiconductor optical amplifier integrated laser of the present application is improved as compared with the conventional semiconductor optical amplifier integrated laser in which the semiconductor optical amplifier portion10does not include the second portion.

FIG.6is a plan view of the semiconductor optical amplifier integrated laser according to a second implementation.FIG.7is an enlarged plan view of the semiconductor optical amplifier portion of the semiconductor optical amplifier integrated laser ofFIG.6. The semiconductor optical amplifier integrated laser shown inFIG.6is the same as the semiconductor optical amplifier integrated laser ofFIG.1except that the width of a mesa unit1′ changes. As in the implementation shown inFIGS.1to5, the solid line defining the mesa1′ represents the contour of the mesa1′, and a common p-i-n structure is formed below the mesa1′.

In the first domain, the mesa unit1′ includes a near end in contact with the second domain20and a far end in contact with the low reflection end surface coating film11. As shown inFIG.7, the far end mesa stripe width W1is narrower than the near end mesa stripe width W2. As shown in the drawing, the mesa stripe width of the mesa unit1′ is gradually narrowed in the first domain from the near end to the far end. Therefore, the mesa unit1′ has a function as a spot size converter (SSC).

By making the width of the far end of the mesa unit1′ narrower than the width of the near end, the photon distribution distributed around the active layer becomes relatively wide, and the far field pattern (FFP) can be narrowed. In the present implementation, the width at the far end is 0.8 times or less the width at the near end in a plan view of the semiconductor optical amplifier integrated laser. Conversely, the width at the far end may be wider than the width at the near end. For example, the width of the far end is 1.2 times or more the width of the near end in a plan view of the semiconductor optical amplifier integrated laser.

FIG.8shows a plan view of an example of a semiconductor optical amplifier integrated laser in which a modulator is integrated. The semiconductor optical amplifier integrated laser shown inFIG.8is the same as the semiconductor optical amplifier integrated laser ofFIG.1except that a semiconductor modulator portion30is provided. The semiconductor optical amplifier integrated laser includes the semiconductor laser oscillator portion20that oscillates light having a predetermined wavelength, the semiconductor optical amplifier portion10that amplifies the laser-oscillated light, and the semiconductor modulator portion30that modulates the amplified laser light. The semiconductor modulator portion30includes an electrode40. The semiconductor modulator portion30modulates the light output from the semiconductor optical amplifier portion10by applying a voltage (modulation signal) to the electrode40, and the modulated light is output from the emission surface on which the low reflection end surface coating film11is formed. The semiconductor modulator portion30may be an electro-absorption modulator or an MZ modulator.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementations to the precise forms disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the implementations.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various implementations includes each dependent claim in combination with every other claim in the claim set.

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Further, as used herein, the article “the” is intended to include one or more items referenced in connection with the article “the” and may be used interchangeably with “the one or more.” Furthermore, as used herein, the term “set” is intended to include one or more items (e.g., related items, unrelated items, a combination of related and unrelated items, etc.), and may be used interchangeably with “one or more.” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Also, as used herein, the term “or” is intended to be inclusive when used in a series and may be used interchangeably with “and/or,” unless explicitly stated otherwise (e.g., if used in combination with “either” or “only one of”).