JP4613374B2 - Semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a semiconductor laser in which a plurality of laser diodes having different oscillation wavelengths are formed on the same substrate, and in particular, a semiconductor in which a coat film for controlling the laser output and protecting the end face is formed on the end face of each laser diode. About laser.
[0002]
[Prior art]
Examples of an optical recording medium (hereinafter referred to as an optical disc) that records or reproduces information by irradiating light include a compact disc (CD), a mini disc (MD), and a digital video disc (DVD). The optical disc as described above is irradiated with light having different wavelengths according to the type of the optical disc. For example, light having a wavelength of 780 nm band is used for reproducing a CD, and light having a wavelength of 650 nm band is used for reproducing a DVD.
[0003]
Therefore, an optical recording / reproducing apparatus compatible with different types of optical disks requires a plurality of light sources having different oscillation wavelengths. In an optical recording / reproducing apparatus, a laser diode is usually used as a light source. However, when a plurality of laser diodes are separately formed, it is difficult to reduce the size of the apparatus, and the manufacturing process is complicated.
In order to solve the above problem, development of a multi-wavelength monolithic semiconductor laser in which a plurality of laser diodes having different oscillation wavelengths are formed on the same substrate is underway.
[0004]
The configuration of the edge-emitting type multi-wavelength semiconductor laser will be described with reference to the perspective view of FIG. 1A and the top view of FIG. The semiconductor laser shown in FIG. 1 emits laser light with a wavelength of 650 nm for DVD reproduction and laser light with a wavelength of 780 nm for CD reproduction on a substrate 1 made of, for example, n-GaAs. And a laser diode B. The distance between the light emitting portion of the laser diode A and the light emitting portion of the laser diode B is often 200 μm or less, for example, about 100 μm.
[0005]
In the laser diode A portion, an n-cladding layer 2a made of, for example, n-AlGaInP, an active layer 3a made of, for example, GaInP, a p-cladding layer 4a, made of, for example, p-AlGaInP, and a p-GaAs, for example, And a cap layer 5a. A high resistance layer is formed on the surface of the p-cladding layer 4a except for the stripe 6a. Although not shown, a p-type electrode is formed on the cap layer 5a, and an n-type electrode is formed on the bottom of the substrate 1.
[0006]
The laser diode B portion includes an n-cladding layer 2b made of, for example, n-AlGaAs, an active layer 3b made of, for example, AlGaAs, a p-cladding layer 4b made of, for example, p-AlGaAs, and a p-GaAs, for example. And a cap layer 5b. A high resistance layer is formed on the surface of the p-cladding layer 4b except for the stripe 6b. Although not shown, a p-type electrode is formed on the cap layer 5b, and an n-type electrode is formed on the bottom of the substrate 1.
[0007]
In the laser diodes A and B, resonators are formed in the active layers 3a and 3b. The high resistance layer is formed by ion-implanting n-type impurities into the surfaces of the p-cladding layers 4a and 4b, and the striped regions 6a and 6b sandwiched between the high resistance layers are left as low resistance layers. By selectively forming the high resistance layer, a gain waveguide structure (current confinement structure) is formed as shown in FIG. 1B, and it is possible to control a current flowing region, that is, a region where optical gain occurs. Become.
[0008]
As shown in FIG. 1B, the laser light L is emitted from the front end face F, but is also partially lost from the rear end face R. The front end face F and the rear end face R that are both ends of the light emitting region (optical waveguide) 7 are mirror surfaces.
In order to make the end surface a mirror surface, the wafer is usually cleaved. Alternatively, the mirror surface may be formed by etching instead of cleaving. In some cases, for example, a coat film made of a dielectric is formed on the cleaved surface for the purpose of controlling the reflectance of the end face or preventing the degradation of the cleaved surface.
[0009]
As a coating film (dielectric film) formed on the end face, for example, Al₂O_Three, Amorphous silicon, SiO₂, Si_ThreeN_FourA single layer film or a multilayer film in which these films are laminated is used. By changing the film thickness of these coat films, the reflectance of the end face can be adjusted. Usually, the front end face F has a low reflectance (for example, 30% or less), and the rear end face R has a high reflectance (for example, 50% or more, preferably 70% or more). Energy conversion efficiency and front / rear output ratio depend on the reflectance of the end face. Therefore, the coat film for controlling the reflectance of the end face is one of important design parameters for the semiconductor laser.
[0010]
When a coat film is formed on the end face, the reflectivity of the end face varies periodically as the coat film thickness increases. When the oscillation wavelength is λ, the reflectance becomes a maximum value or a minimum value when the thickness of the coating film formed on the end face is designed based on λ / 4 or a multiple thereof. Therefore, it is possible to minimize the variation in reflectance due to film formation variation and the like.
For example, in the laser diode A of FIG. 1, the oscillation wavelength λ is 650 nm and the refractive index n₁Al is 1.62₂O_ThreeIs used to form the dielectric film 8 on the front end face F, the film thickness d of the dielectric film 8₈The
d₈= (Λ / 2) / n₁≒ 200.6 (nm) (1)
Or, if it is a multiple thereof, a stable reflectance can be obtained.
[0011]
The rear end face R needs to have a high reflectivity, but the Al₂O_ThreeAnd the like are used in a single layer, the reflectance is less than 50% in all cases, so that a multilayer coating film is formed. For example, in the laser diode A of FIG. 1, the oscillation wavelength λ is 650 nm, and the first dielectric film 9a is, for example, Al.₂O_ThreeFor example, when an amorphous silicon film is formed as the second dielectric film 9b, the film thickness of each layer is determined as follows, for example.
[0012]
Refractive index n₁Al is 1.62₂O_ThreeFilm thickness d_9aThe
d_9a= (Λ / 4) / n₁≒ 100.3 (nm) (2)
Or its multiple, and the refractive index n₂The film thickness d of the amorphous silicon film having a value of 3.25_9bThe
d_9b= (Λ / 4) / n₂≒ 50.0 (nm) (3)
Or a multiple thereof.
As described above, by determining the film thickness of the dielectric film formed on the end face based on an integral multiple of λ / 4 or a combination thereof, the film thickness and refraction caused by variations in the film formation of the dielectric film, etc. Even when there is a variation in rate, a stable reflectance can be obtained.
[0013]
[Problems to be solved by the invention]
In the case of a multiwavelength monolithic semiconductor laser, ideally, it is desirable to form a dielectric film according to the above-described conventional design on each of laser diodes having different oscillation wavelengths.
However, in that case, it is necessary to perform end surface coating a plurality of times, which complicates the manufacturing process.
[0014]
For example, when a laser diode for CD playback and a laser diode for DVD playback are formed on the same substrate, the end face of the laser diode for DVD (wavelength 650 nm band) is masked first, for example. Then, a dielectric film is formed on the end face of the laser diode for CD (wavelength 780 nm band). Thereafter, the masking of the end face of the DVD laser diode is removed, the end face of the CD laser diode is masked, and a dielectric film is formed on the end face of the DVD laser diode. Such end face coating needs to be performed on both the front end face and the rear end face. Since a multilayer dielectric film is usually formed on the rear end face, the number of manufacturing steps is particularly increased.
[0015]
In order to avoid an increase in the number of manufacturing steps as described above, there is also a method of matching the optimum wavelength of the end face coat with one laser diode and simultaneously forming the end face coat on a plurality of laser diodes on the same substrate. However, in this case, a laser diode having a wavelength as a design reference can provide a stable reflectance with respect to film formation variation, but the other laser diode sacrifices the reflectance stability with respect to film formation variation. .
[0016]
In each of a plurality of monolithically formed laser diodes, a predetermined value (imaginary wavelength) between the minimum value and the maximum value among the oscillation wavelengths of the laser diode is used in order to reduce the variation in the reflectance of the dielectric film on the end face. A method for designing a coating film based on the above) is also conceivable. For example, if the thickness of the coating film is optimized with respect to the wavelength that is the arithmetic average value of the oscillation wavelengths of each laser diode, the variation in the reflectance of the end face in each laser diode is moderately suppressed, and once With this end face coating, a coat film can be formed on the end faces of a plurality of laser diodes.
[0017]
However, according to the design of the end face coat that is adjusted to the arithmetic average value of each oscillation wavelength or the wavelength substantially in the middle of each oscillation wavelength as described above, the reflectance at each oscillation wavelength is a value near the extreme value. Since it cannot be an extreme value, fluctuations in reflectance may be a problem. In particular, when the wavelength difference between the oscillation wavelengths is large, the deviation of the reflectance from the extreme value becomes large, so that the reflectance fluctuation due to film formation variation or the like is likely to be remarkable. Further, even when the oscillation wavelength is a short wavelength, the variation in reflectance tends to be large.
[0018]
As described above, in the multi-wavelength monolithic semiconductor laser, in order to form the end face coat that minimizes the variation in reflectivity on each laser diode, an operation such as masking is required, which increases the number of manufacturing steps. However, if an end face coat having a common film thickness is applied to a plurality of laser diodes having different oscillation wavelengths, the manufacturing process can be prevented from becoming complicated, but the reflectance variation cannot be sufficiently suppressed.
[0019]
  The present invention has been made in view of the above problems. Therefore, the present invention can emit a plurality of laser beams having different oscillation wavelengths by forming a plurality of active layers having different materials and compositions on the same substrate. It is an object of the present invention to provide a semiconductor laser in which a dielectric film with little variation in reflectance is formed on end faces of a plurality of active layers..
[0020]
[Means for Solving the Problems]
  According to the present invention, formed on the same semiconductor substrate.EachHas multiple active layers with different compositions and emits multiple laser beams with different oscillation wavelengthsHave multiple laser regionsA semiconductor laser,
  Specify the mirror surface,Of the plurality of laser regionsLaser beam emission sideAfterendOn the faceA plurality of films with different refractive indexes,The plurality of laser regionsOne common coating film for
  The coating film formed by laminating the plurality of films is formed by controlling the optical film thickness so that the reflectance becomes an extreme value with respect to the plurality of wavelengths of the plurality of laser beams.
  A semiconductor laser is provided.
[0021]
  Preferably, in the semiconductor laser of the present invention,The coat film formed by laminating the plurality of films has a number of layers j (j is2 or moreNatural number), the number of the oscillation wavelengths is k (k is a natural number of 2 or more), and the oscillation wavelength is λ._i(I2To natural k), oscillation wavelength λ_iThe refractive index of the coating film of the jth layer at n is n_ijThe film thickness of the j-th coat film is d_jThe oscillation wavelength λ_iIn eachThe following formula holds.
  Σn_ij・ D_j/ Λ_i= M_i/ 4
    (M_iIs an integer)
[0022]
In the semiconductor laser of the present invention, preferably, when the number k of the oscillation wavelengths is 2, and a and b are integers,
λ₁= A (λ₂−λ₁) And λ₂= B (λ₂−λ₁)
It is characterized by that.
[0023]
The semiconductor laser of the present invention is preferably characterized in that the coating film is made of a dielectric.
The semiconductor laser of the present invention is preferably characterized in that at least one layer of the coating film has a wavelength dispersion characteristic in which a refractive index changes depending on the wavelength at the oscillation wavelength and a wavelength in the vicinity thereof. . More preferably, in the semiconductor laser of the present invention, the coating film having the wavelength dispersion characteristic at the oscillation wavelength and a wavelength in the vicinity thereof is TiO 2.₂System, SrTiO_Three, Chalcogenite, LiNbO_ThreeLiNbO-based, PbTiO-based, PLZT-based (Pb_yLa_1-yZr_xTi_1-xO_Three), KTP (KTiOPO_Four) Is contained.
[0024]
In the semiconductor laser of the present invention, preferably, the number k of the oscillation wavelengths is 2, m.₂-M₁Is an even number, and the oscillation wavelength λ₁, Λ₂Both of the reflectances at the maximum are maximum values.
Alternatively, in the semiconductor laser of the present invention, preferably, the number k of the oscillation wavelengths is 2, m.₂-M₁Is an odd number, and the oscillation wavelength λ₁, Λ₂One of the reflectances in the above is a maximum value and the other is a minimum value.
[0025]
In the semiconductor laser of the present invention, preferably, the number k of the oscillation wavelengths is 2, and the oscillation wavelength λ₁, Λ₂Are in the vicinity of 650 nm and 780 nm, respectively. Alternatively, in the semiconductor laser of the present invention, preferably, the number k of the oscillation wavelengths is 2, and the oscillation wavelength λ₁, Λ₂Are in the vicinity of 780 nm and 840 nm, respectively. Alternatively, in the semiconductor laser of the present invention, preferably, the number k of the oscillation wavelengths is 2, and the oscillation wavelength λ₁, Λ₂Are in the vicinity of 840 nm and 980 nm, respectively. Alternatively, in the semiconductor laser of the present invention, preferably, the number k of the oscillation wavelengths is 2, and the oscillation wavelength λ₁Near 405 nm, λ₂Is in the vicinity of 675 nm or 630 nm. Alternatively, in the semiconductor laser of the present invention, preferably, the number k of the oscillation wavelengths is 2, and the oscillation wavelength λ₁, Λ₂Are in the vicinity of 520 nm and 650 nm, respectively. Alternatively, in the semiconductor laser of the present invention, preferably, the number k of the oscillation wavelengths is 2, and the oscillation wavelength λ₁Near 360 nm, λ₂Is in the vicinity of 420 nm or 405 nm.
[0026]
In the semiconductor laser of the present invention, preferably, the reflectance at at least one of the oscillation wavelengths is as low as or less than that when the coating film is not formed, and at at least one other oscillation wavelength. The reflectance is relatively high. More preferably, the semiconductor laser of the present invention is characterized in that the low reflectance is approximately 30% or less and the high reflectance is approximately 50% or more.
The semiconductor laser of the present invention is preferably characterized in that the active layer is formed at a junction between the first conductivity type cladding layer and the second conductivity type cladding layer. The semiconductor laser of the present invention is preferably characterized in that the active layer has a current confinement structure.
[0027]
This makes it possible to stabilize the reflectance of the end face in each of a plurality of laser diodes having different oscillation wavelengths formed on the same substrate. According to the semiconductor laser of the present invention, since the coat film having a common film thickness is formed in each laser diode, the manufacturing process can be simplified. Further, since the film thickness of the coat film is optimized for each oscillation wavelength, a stable reflectance can be obtained even when the film thickness or refractive index varies due to film formation variation.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a semiconductor laser and a coating film for optical parts of the present invention will be described below with reference to the drawings.
(Embodiment 1)
FIG. 1A is a perspective view of the semiconductor laser of this embodiment, and FIG. 1B is a corresponding top view. The semiconductor laser shown in FIG. 1 emits laser light with a wavelength of 650 nm for DVD reproduction and laser light with a wavelength of 780 nm for CD reproduction on a substrate 1 made of, for example, n-GaAs. And a laser diode B. The distance between the light emitting portion of the laser diode A and the light emitting portion of the laser diode B is often 200 μm or less, for example, about 100 μm.
[0031]
In the laser diode A portion, an n-cladding layer 2a made of, for example, n-AlGaInP, an active layer 3a made of, for example, GaInP, a p-cladding layer 4a, made of, for example, p-AlGaInP, and a p-GaAs, for example, And a cap layer 5a. A high resistance layer is formed on the surface of the p-cladding layer 4a except for the stripe 6a. Although not shown, a p-type electrode made of a laminated film of Ti / Pt / Au is formed on the cap layer 5a.
[0032]
The laser diode B portion includes an n-cladding layer 2b made of, for example, n-AlGaAs, an active layer 3b made of, for example, AlGaAs, a p-cladding layer 4b made of, for example, p-AlGaAs, and a p-GaAs, for example. And a cap layer 5b. A high resistance layer is formed on the surface of the p-cladding layer 4b except for the stripe 6b. Although not shown, a p-type electrode made of a laminated film of Ti / Pt / Au is formed on the cap layer 5b. Further, in common with the laser diode A portion and the laser diode B portion, an n-type electrode made of a laminated film of AuGe / Ni / Au is formed under the substrate 1.
[0033]
In the laser diodes A and B, resonators are formed in the active layers 3a and 3b. The high resistance layer is formed by ion-implanting n-type impurities into the surfaces of the p-cladding layers 4a and 4b, and the striped regions 6a and 6b sandwiched between the high resistance layers are left as low resistance layers. By selectively forming the high resistance layer, a gain waveguide structure (current confinement structure) is formed as shown in FIG. 1B, and it is possible to control a current flowing region, that is, a region where optical gain occurs. It has become.
[0034]
As shown in FIG. 1B, the front end face F has a refractive index n common to the laser diode A portion and the laser diode B portion.₁Al is 1.62₂O_ThreeThe film thickness d₈A dielectric film 8 having a thickness of 1204 nm is formed.
In addition, the rear end face R is common to the laser diode A part and the laser diode B part.₂O_ThreeFilm thickness d_9aA first dielectric film 9a having a thickness of 1100 nm is formed. Furthermore, the refractive index n on the surface₂Is made of amorphous silicon having a thickness of 3.25, and the film thickness d_9bA second dielectric film 9b having a thickness of 50 nm is formed. These dielectric films 8, 9a, 9b are formed by a method such as sputtering.
According to the semiconductor laser of this embodiment, the film thicknesses of the dielectric film 8 on the front end face and the dielectric films 9a and 9b on the rear end face are such that the reflectance at the oscillation wavelengths of the laser diodes A and B is maximized. Is set to
[0035]
FIG. 2A shows the relationship between the film thickness of the dielectric film 8 formed on the front end face of the semiconductor laser of this embodiment and the reflectance. Further, FIG. 2B shows the relationship between the wavelength and the reflectance at the front end face on which the dielectric film 8 is formed. FIG. 2 shows a laser diode A (oscillation wavelength λ₁= 650 nm) resonator refractive index 3.45, laser diode B (oscillation wavelength λ₂= 780 nm) is a result of calculation with the refractive index of the resonator of 3.59 being set.
[0036]
Laser diode A (oscillation wavelength λ₁= 650 nm), the film thickness d of the dielectric film 8 is derived from the above-described equation (1).₈Is 200.6 nm and multiples thereof, the reflectance becomes maximum. From similar calculations, laser diode B (oscillation wavelength λ₂= 780 nm), the thickness of the dielectric film 8₈Is 240.7 nm and multiples thereof, the reflectance becomes maximum.
As shown in FIG. 2A, when the thickness of the dielectric film 8 is approximately 1200 nm, the phase shift due to the difference between the two oscillation wavelengths is 2π. The relationship between the wavelength and the reflectance at this time is shown in FIG. As shown in FIG. 2 (b), the reflectance is maximized at any of the oscillation wavelengths of the laser diodes A and B. Therefore, fluctuations in reflectivity are suppressed in both laser diodes.
[0037]
Where the oscillation wavelength λ₁, Λ₂And the film thickness d that maximizes the reflectance.₈The following relationship holds between n₁Is λ₁And λ₂Al in₂O_ThreeIs the refractive index.
n₁・ D₈/ Λ₁= M₁/ 4 (m₁Is an integer) (4)
n₁・ D₈/ Λ₂= M₂/ 4 (m₂Is an integer) (5)
Also, λ₁And λ₂Almost satisfies the following relationship.
λ₁= A (λ₂−λ₁) And λ₂= B (λ₂−λ₁)
(A and b are integers) (6)
m₁-M₂Is an even number, the oscillation wavelength λ₁, Λ₂In contrast, the reflectance is a maximum value. m₁-M₂Is an odd number, the oscillation wavelength λ₁, Λ₂The reflectance is a maximum value for one of the two, and the reflectance is a minimum value for the other.
[0038]
When the oscillation wavelengths of a plurality of laser diodes formed on the same substrate satisfy the above relationships (4) to (6), the reflectance of the end face of each laser diode can be set to an extreme value. Therefore, also in the case of other combinations of oscillation wavelengths that have been put into practical use, it is possible to prevent the reflectance from being fluctuated due to film formation variations and the like, as in the case of the present embodiment.
For example, the combination of laser diode oscillation wavelengths is λ₁= 780 nm, λ₂= 840nm or λ₁= 840 nm, λ₂The same effect can be obtained also when 980 nm.
[0039]
In addition, for monolithic lasers that emit laser beams having three or more different oscillation wavelengths, if the relationships (4) to (6) are satisfied, fluctuations in reflectance at each oscillation wavelength can be similarly prevented. it can.
In the above-described embodiment, λ also occurs when the thickness of the dielectric film 8 is a multiple of 1200 nm.₁, Λ₂In both cases, the reflectance becomes a maximum, but it is preferable to set the minimum value among the plurality of film thicknesses with which the same reflectance can be obtained. Thereby, it is possible to shorten the film formation time and increase the production efficiency, and it is possible to prevent the film formation variation from becoming remarkable due to the increase in the film thickness.
[0040]
(Embodiment 2)
In the semiconductor laser according to the first embodiment, if a material having wavelength dispersion is used for the dielectric film 8 on the front end face, the dielectric film 8 can be thinned. Al of Embodiment 1₂O_ThreeFor example, TiO₂System materials (refractive index n at a wavelength of 650 nm_3a= 2.457, refractive index n at a wavelength of 780 nm_3bFIG. 3A shows the relationship between the film thickness of the dielectric film 8 and the reflectance in the case of using (= 2.36).
[0041]
From the calculation similar to the above-described equation (1), the laser diode A (oscillation wavelength λ₁= 650 nm), the film thickness d of the dielectric film 8₈Is 132.3 nm and multiples thereof, the reflectance becomes maximum. Laser diode B (oscillation wavelength λ₂= 780 nm), the film thickness d of the dielectric film 8₈Is 165.3 nm and multiples thereof, the reflectance becomes maximum.
[0042]
As shown in FIG. 3A, when the film thickness of the dielectric film 8 is approximately 661 nm, the phase shift due to the difference between the two oscillation wavelengths is 2π. The relationship between the wavelength and the reflectance at this time is shown in FIG. As shown in FIG. 3 (b), the reflectance is maximized at any of the oscillation wavelengths of the laser diodes A and B. Therefore, fluctuations in reflectivity are suppressed in both laser diodes.
[0043]
Also in the case of this embodiment, the relationships shown in the equations (4) to (6) of the first embodiment are satisfied. In particular,
n_3a・ D₈/ Λ₁= M₁/ 4 (m₁Is an integer) ... (4 ')
n_3b・ D₈/ Λ₂= M₂/ 4 (m₂Is an integer) ... (5 ')
λ₁= A (λ₂−λ₁) And λ₂= B (λ₂−λ₁)
(A and b are integers) (6)
It becomes. Even when a material with wavelength dispersion is used, if the optical length (optical film thickness) at each oscillation wavelength is an integral multiple of λ / 4 from the viewpoint of phase difference, fluctuations in reflectance are prevented. Can do.
According to the present embodiment, the dielectric film 8 is made thinner than in the first embodiment. Therefore, the film formation time can be shortened by appropriately selecting the film type.
[0044]
(Embodiment 3)
FIG. 4A shows the relationship between the film thickness of the dielectric films 9a and 9b formed on the rear end face and the reflectance of the semiconductor laser of the first embodiment shown in FIG. FIG. 4B shows the relationship between the wavelength and the reflectance of the rear end face on which the dielectric films 9a and 9b are formed.
As described above, the first dielectric film 9a is made of Al.₂O_Three(Refractive index n₁= 1.62), and the film thickness is 1100 nm. The second dielectric film 9b is made of amorphous silicon (refractive index n₂= 3.25), and the film thickness is 50 nm.
[0045]
As described in the first embodiment, the first layer of Al₂O_ThreeFor the film, the oscillation wavelength λ₁= Film thickness d for 650 nm_9aIs 200.6 nm and multiples thereof, the reflectance becomes maximum, and the oscillation wavelength λ₂= Film thickness d for 780 nm_9bIs 240.7 nm and multiples thereof, the reflectance becomes maximum. Therefore, there is a difference of about 40 nm in the film thickness at which the maximum value of the reflectance is obtained, and it is difficult to stabilize the reflectance for both oscillation wavelengths.
[0046]
On the other hand, according to the present embodiment, by setting the thickness of the first dielectric film 9a to 1100 nm, the oscillation wavelength λ₁, Λ₂The reflectivity is almost minimal for each of the above, and the phase shift due to the difference between the two oscillation wavelengths is close to 2π. Further, for the second amorphous silicon film 9b, as shown in the equation (3), the oscillation wavelength λ₁The reflectance becomes maximum when the film thickness is 50.0 nm with respect to 650 nm. From the same calculation, the oscillation wavelength λ₂For = 780 nm, the reflectance is maximized when the film thickness is 60.0 nm.
[0047]
Here, in the present embodiment, the relationship shown below is λ₁And λ₂(I = 1 or 2) is satisfied respectively.
Σn_ij・ D_j/ Λ_i= M_i/ 4 (m_iIs an integer) (7)
(However, n_ijIs the oscillation wavelength λ_iRepresents the refractive index of the dielectric film of the jth layer at_jRepresents the thickness of the jth dielectric film. )
In addition, the relationship of the above-described equation (6) is also established.
[0048]
FIG. 4B shows the relationship between the wavelength and the reflectance when the dielectric film on the rear end face has the above configuration. As shown in FIG. 4B, the reflectivity is almost maximized at any oscillation wavelength of the laser diodes A and B, and the fluctuation of the reflectivity is suppressed. Therefore, a stable reflectance of 70% or more can be obtained for both the laser diodes A and B.
[0049]
(Embodiment 4)
When the coating film formed on the end face is a multilayer, the film thickness of the second dielectric film can be made larger than the film thickness of the first dielectric film, contrary to the third embodiment. For example, in the first layer, Al₂O_ThreeFIG. 5A shows the relationship between the film thickness and the reflectance when the film is 110 nm thick and the second layer is an amorphous silicon film having a film thickness of 540 nm. As shown in FIG. 5A, by combining the film thicknesses of the dielectric films 9a and 9b with the above combination, the oscillation wavelength λ₁= 650 nm, oscillation wavelength λ₂The reflectance can be almost maximized for both of = 780 nm.
[0050]
As shown in the equation (2), the first dielectric film (Al₂O_ThreeFilm) 9a, the oscillation wavelength λ₁When the film thickness is 100.3 nm and multiples of 650 nm, the reflectance is minimal. From a similar calculation, the oscillation wavelength λ₂For = 780 nm, the reflectance is minimal when the film thickness is 120.4 nm and multiples thereof. Al₂O_ThreeBy setting the film thickness of the film 9a to 110 nm, the oscillation wavelength λ₁, Λ₂In both cases, the reflectance is in the vicinity of the minimum value.
[0051]
Further, for the second dielectric film (amorphous silicon film) 9b, as shown in the equation (3), the oscillation wavelength λ₁When the film thickness is 50.0 nm and an odd multiple of 650 nm, the reflectance becomes maximum. From the same calculation, the oscillation wavelength λ₂For = 780 nm, the reflectance is maximized when the film thickness is 60.0 nm and an odd multiple thereof. By setting the thickness of the amorphous silicon film 9b to 540 nm, the phase shift due to the difference between the two oscillation wavelengths becomes approximately 2π. Also, the oscillation wavelength λ₁, Λ₂In both cases, the reflectance is almost a maximum value.
[0052]
FIG. 5B shows the relationship between the wavelength and the reflectance when the dielectric film on the rear end face has the above configuration. As shown in FIG. 5 (b), the reflectivity is almost maximized at any oscillation wavelength of the laser diodes A and B, and the fluctuation of the reflectivity is suppressed. Therefore, a stable reflectance of 70% or more can be obtained for both the laser diodes A and B.
[0053]
According to the present embodiment, the total film thickness of the dielectric films 9a and 9b formed on the rear end face is 650 nm, and the dielectric film is thinned to almost half compared to 1150 nm in the third embodiment. Can do. Therefore, depending on the combination of the constituent materials of the dielectric film, the film formation time can be shortened.
[0054]
(Embodiment 5)
In the dielectric film formed on the rear end face of the third embodiment, if the dielectric film 9a or 9b is made of a material having wavelength dispersion, the dielectric film can be thinned. The first dielectric film (Al₂O_ThreeFilm) 9a, for example, TiO₂System materials (refractive index n at a wavelength of 650 nm_4a= 2.337, refractive index n at a wavelength of 780 nm_4b= 2.316) and the film thickness was 760 nm. The second dielectric film 9b is made of amorphous silicon (refractive index n₂= 3.25). FIG. 6A shows the relationship between the film thickness of the dielectric films 9a and 9b and the reflectance in this case.
[0055]
From the same calculation as the above-described equation (1), the laser diode A (the oscillation wavelength λ₁= 650 nm) for the first dielectric film (TiO₂Film) film thickness d of 9a_9aIs 139.1 nm and multiples thereof, the reflectance becomes maximum. Laser diode B (oscillation wavelength λ₂= 780 nm) for TiO₂Film thickness d of film 9a_9aIs 168.4 nm and multiples thereof, the reflectance becomes maximum. As shown in FIG. 6 (a), TiO₂When the film thickness of the film 9a is approximately 760 nm, the oscillation wavelength λ₁, Λ₂Thus, the reflectance is almost minimal, and the phase shift due to the difference between the two oscillation wavelengths is 2π.
[0056]
Further, for the second amorphous silicon film 9b, as shown in the equation (3), the oscillation wavelength λ₁= Film thickness d for 650 nm_9bWhen the thickness is 50.0 nm, the reflectance becomes maximum. From the same calculation, the oscillation wavelength λ₂For = 780 nm, the film thickness d_9bWhen the thickness is 60.0 nm, the reflectance becomes maximum. Therefore, the film thickness d of the dielectric film 9b_9bIs 55 nm and the total thickness of 9a and 9b is 815 nm.₁, Λ₂For both, the reflectivity is almost maximal.
[0057]
FIG. 6B shows the relationship between the wavelength and the reflectance when the dielectric film on the rear end face has the above configuration. As shown in FIG. 6 (b), the reflectance is almost maximized at both oscillation wavelengths of the laser diodes A and B, and the fluctuation of the reflectance is suppressed. Therefore, a stable reflectance can be obtained for both the laser diodes A and B.
[0058]
Also in the case of this embodiment, the relationship shown in the expression (6) of the first embodiment and the expression (7) of the third embodiment is satisfied. Also for the rear end face, a material having wavelength dispersion can be used if the optical length at each oscillation wavelength is an integral multiple of λ / 4 from the viewpoint of phase difference.
According to the present embodiment, the total thickness of the dielectric films 9a and 9b can be reduced as compared with the third embodiment. Therefore, the film formation time can be shortened depending on the combination of film types or the film formation method.
[0059]
(Embodiment 6)
In the first to fifth embodiments, the oscillation wavelength λ₁, Λ₂In the case of multilayer coating, the reflectance for each oscillation wavelength can be made different by controlling the film thickness of the first dielectric film. .
For example, Al shown in Embodiment 3₂O_ThreeIn a film configuration in which a film and an amorphous silicon film are laminated, Al₂O_ThreeThe example which changed the film thickness of the film | membrane is shown to Fig.7 (a) and (b). FIG. 7A shows Al.₂O_ThreeFIG. 7 (b) shows the relationship between the wavelength and the reflectance when the film thickness is 1010 nm.₂O_ThreeThe relationship between the wavelength and the reflectance when the film thickness is 960 nm is shown.
In both FIGS. 7A and 7B, a high reflectance of 50% or more is realized at one oscillation wavelength, which is slightly higher than 30%, which is substantially equal to the non-coated end face reflectance.
[0060]
When the reflectance of the end face is changed, the differential efficiency also changes in addition to the oscillation threshold current in the laser characteristics, so that the operating current is also affected. Thereby, it becomes possible to adjust to the characteristic according to a use.
For example, if the reflectance of the rear end face is increased, more light can be emitted from the front end face, which is suitable for a high-power laser. On the other hand, when the reflectance of the front end face is increased, output fluctuation due to return light is suppressed, so that an isolator becomes unnecessary. Further, when the reflectances at both the front and rear end faces are increased, the oscillation threshold current can be lowered and the differential efficiency can be lowered accordingly, so that output control is facilitated.
[0061]
The embodiment of the semiconductor laser of the present invention is not limited to the above description. For example, in the above-described embodiment, the case of a combination of wavelengths in the 650 nm band and the 780 nm band has been described, but other wavelength combinations may be used. Further, it can be applied to a broad area type, vertical cavity type semiconductor laser, or the like. The waveguide structure of the active layer is not limited to the current confinement structure, and may be another structure such as a refractive index waveguide structure.
Moreover, it becomes easy to control the reflectance of the optical component by forming the end surface coat provided in the semiconductor laser of the present invention on the surface of the optical component that transmits light of a plurality of specific wavelengths.
In addition, various modifications can be made without departing from the scope of the present invention.
[0062]
【The invention's effect】
According to the semiconductor laser of the present invention, in a semiconductor laser capable of emitting a plurality of laser beams having different oscillation wavelengths, fluctuations in the reflectance of the end face of the active layer are suppressed, and the output of the laser beam is stabilized at each oscillation wavelength. It becomes possible.
According to the coating film for an optical component of the present invention, it is possible to easily control the reflectance of the surface by suppressing the fluctuation of the reflectance of the surface in the optical component that transmits light of a plurality of specific wavelengths. Become.
[Brief description of the drawings]
FIG. 1A is a perspective view of a conventional semiconductor laser according to Embodiments 1 to 6 of the present invention, and FIG. 1B is a corresponding top view.
2A is a diagram showing a relationship between a film thickness of a dielectric film formed on a front end surface of a semiconductor laser and a reflectance according to Embodiment 1 of the present invention, and FIG. It is a figure which shows the relationship.
3A is a diagram illustrating a relationship between a film thickness of a dielectric film formed on a front end surface of a semiconductor laser and a reflectance according to Embodiment 2 of the present invention, and FIG. 3B is a diagram illustrating a wavelength and a reflectance. It is a figure which shows the relationship.
4A is a diagram showing a relationship between a film thickness of a dielectric film formed on a rear end face of a semiconductor laser and a reflectance according to Embodiment 3 of the present invention, and FIG. It is a figure which shows the relationship.
5A is a diagram showing a relationship between a film thickness of a dielectric film formed on a rear end face of a semiconductor laser and a reflectance according to Embodiment 4 of the present invention, and FIG. It is a figure which shows the relationship.
6A is a diagram illustrating a relationship between a film thickness of a dielectric film formed on a rear end face of a semiconductor laser and a reflectance, and FIG. 6B is a diagram illustrating a wavelength and a reflectance according to Embodiment 5 of the present invention; It is a figure which shows the relationship.
FIGS. 7A and 7B are diagrams showing a relationship between wavelength and reflectance according to Embodiment 6 of the present invention. FIGS.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate, 2a, 2b ... n-cladding layer, 3a, 3b ... Active layer, 4a, 4b ... p-cladding layer, 5a, 5b ... Cap layer, 6a, 6b ... Stripe, 7 ... Light emitting region (optical waveguide) , 8... Dielectric film on the front end face, 9a. First dielectric film on the rear end face, 9b. Second dielectric film on the rear end face.

Claims (18)

A semiconductor laser having a plurality of laser regions formed on the same semiconductor substrate , each having a plurality of active layers having different compositions, and emitting a plurality of laser beams having different oscillation wavelengths,
Defining a mirror surface, the end plane of the laser beam exit side of said plurality of laser regions, with different refractive index, by laminating a plurality of films, the one common to the plurality of laser regions coat Having a membrane,
The coating film formed by laminating the plurality of films is formed by controlling the optical film thickness so that the reflectance becomes an extreme value with respect to the plurality of wavelengths of the plurality of laser beams.
Semiconductor laser. The coat film formed by laminating the plurality of films has a number of layers j (j is a natural number of 2 or more ), the number of oscillation wavelengths is k (k is a natural number of 2 or more), and the oscillation wavelength is λ _i (i is a natural number from 2 to k), the refractive index n _ij of the j th layer coating film at the oscillation wavelength lambda _i, when the thickness of the j th layer coated film was d _j, at the oscillation wavelength lambda _i Respectively,
Σn _ij · d _j / λ _i = m _i / 4
( _Mi is an integer)
The semiconductor laser according to claim 1. When the number k of the oscillation wavelengths is 2 and a and b are integers,
λ ₁ = a (λ ₂ −λ ₁ ), and
λ ₂ = b (λ ₂ −λ ₁ )
Holds,
The semiconductor laser according to claim 2. The coating film is made of a dielectric;
The semiconductor laser according to claim 2. At least one layer of the coating film formed by laminating the plurality of layers has a wavelength dispersion characteristic in which a refractive index changes depending on the wavelength at the oscillation wavelength and a wavelength in the vicinity thereof.
The semiconductor laser according to claim 2. The coating film having the wavelength dispersion characteristic at the oscillation wavelength and the wavelength in the vicinity thereof is a TiO ₂ type, SrTiO ₃ type, chalcogenite type, LiNbO type including LiNbO ₃ , PbTiO type, PLZT type (Pb _y La _{1− y Zr x Ti 1-x O} 3), containing either KTP (KTiOPO _4),
The semiconductor laser according to claim 5. The number k of the oscillation wavelengths is 2, m ₂ −m ₁ is an even number, and the reflectances at the oscillation wavelengths λ ₁ and λ ₂ are both maximum values.
The semiconductor laser according to claim 2. The number of oscillation wavelengths k is 2, m ₂ −m ₁ is an odd number, _one of the reflectances at the oscillation wavelengths λ ₁ and λ ₂ is a maximum value, and the other is a minimum value.
The semiconductor laser according to claim 2. The number k of the oscillation wavelengths is 2, and the oscillation wavelengths λ ₁ and λ ₂ are in the vicinity of 650 nm and 780 nm, respectively.
The semiconductor laser according to claim 3. The number k of the oscillation wavelengths is 2, and the oscillation wavelengths λ ₁ and λ ₂ are in the vicinity of 780 nm and 840 nm, respectively.
The semiconductor laser according to claim 3. The number k of the oscillation wavelengths is 2, and the oscillation wavelengths λ ₁ and λ ₂ are in the vicinity of 840 nm and 980 nm, respectively.
The semiconductor laser according to claim 3. The number k of the oscillation wavelengths is 2, the oscillation wavelength λ ₁ is in the vicinity of 405 nm, and λ ₂ is in the vicinity of 675 nm or 630 nm.
The semiconductor laser according to claim 3. The number k of the oscillation wavelengths is 2, and the oscillation wavelengths λ ₁ and λ ₂ are in the vicinity of 520 nm and 650 nm, respectively.
The semiconductor laser according to claim 3. The number k of the oscillation wavelengths is 2, the oscillation wavelength λ ₁ is in the vicinity of 360 nm, and λ ₂ is in the vicinity of 420 nm or 405 nm.
The semiconductor laser according to claim 3. The reflectance at at least one of the oscillation wavelengths is a low reflectance equal to or less than that when the coating film is not formed, and the reflectance at at least one other oscillation wavelength is relatively high. ,
The semiconductor laser according to claim 2. The low reflectance is approximately 30% or less, and the high reflectance is approximately 50% or more.
The semiconductor laser according to claim 15. The active layer is formed at a junction between the first conductivity type cladding layer and the second conductivity type cladding layer,
The semiconductor laser according to claim 1. The active layer has a current confinement structure;
The semiconductor laser according to claim 1.

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