This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-278289, filed on Sep. 24, 2004; the entire contents of which are incorporated herein by reference.
A conventional DVD (digital versatile disc) recorder is equipped to play and record CDs. The conventional DVD recorder has a 650 nm high power red laser for playing and recording DVDs and a 780 nm low power infrared laser for playing CDs.
Recently, a monolithic laser element that emits usable light is shown in Japanese patent laid open No. 2004-87564. However, the suitable cavity length of resonator is different between a 650 nm laser and a 780 nm laser.
A semiconductor laser having two different cavity lengths of resonators is shown in the Japanese patent laid open No. H4-245494.
When this semiconductor laser is mounted on a submount with a junction down, the stress on the long resonator and the stress on the short resonator are not even.
This is because the contact area to the submount for the two different length resonators is different. The stress is concentrated to a laser having the short resonator. This may adversely affect the characteristics of one of the lasers.
Aspects of the present invention address one or more of the issues associated with conventional laser arrays.
Embodiments of the present invention will be explained with reference to the drawings.
It is noted that various connections are set forth between elements in the following description. It is noted that these connections in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect.
In at least one aspect of the present invention, a semiconductor laser array may include a substrate; a first laser element on the substrate, the first laser element having a first resonator; a second laser element on the substrate, the second laser element having a second resonator, the second resonator being shorter in cavity length than the first resonator; and a protrusion on the substrate, the protrusion being substantially equal in height from the substrate with one of the first laser element and the second laser element.
Another aspect of the present invention may include semiconductor laser array having a substrate, a first laser element on the substrate, the first laser element having a first resonator, a second laser element on the substrate, the second laser element having a second resonator, the second resonator being shorter in cavity length than the first resonator, and a supporting member on the substrate, the supporting member being separated from the first laser element by a first trench and the supporting member being separated from the second laser element by a second trench.
A further aspect of the present invention may include a semiconductor laser device having a submount; a semiconductor laser array mounted on the submount, the semiconductor laser array having; a substrate, a first laser element on the substrate having a first resonator, the first laser element provided between the submount and the substrate, and a second laser element on the substrate having a second resonator, the second resonator being shorter in cavity length than the first resonator, the second laser element provided between the submount and the substrate; a supporting member provided between the submount and the substrate of the semiconductor laser array.
A first embodiment of the present invention will be explained hereinafter with reference to
As shown in
Protrusion 14 may also be described as a structure separated from the laser elements 12 and 13.
The visible laser element 12 and the infrared laser element 13 are provided in the vicinity of each other so that an optical axis of the visible laser element 12 and the infrared laser element 13 are substantially parallel. The visible laser element 12 and the infrared laser element 13 are separated by a trench 15. The trench 15 may be provided on the substrate 11.
The protrusion 14 may be separated to visible laser element 12 by the trench 15 and to the infrared laser element 13 by a trench 16.
A cavity length L1 of resonator of the visible laser element 12 may be designed so that the visible laser element 12 may be able to emit a high power laser. A cavity length L2 of resonator of the infrared laser element 13 may be designed so that a threshold current (Ith) of the infrared laser element 13 may be reduced.
The cavity length L1 is longer than the cavity length L2. The cavity lengths L1 and L2 may alternatively be described as lengths along the laser resonators' axes (optical axes). Further, these lengths may be alternatively described as in the direction of the light output from each laser.
An n-side electrode 17 may be provided on the back surface of the substrate 11.
A p-side electrode 18 and a p-side electrode 19 are provided on the top surface of the visible laser element 12 and infrared laser element 13, respectively. The n-side electrode 17 and the p-side electrodes 18, 19 are provided for injecting current into an active layer of the visible laser element 12 and infrared laser element 13.
An insulating layer 20 may be provided on the top surface of the protrusion 14.
The insulating layer 20 is used to prevent injecting of current into active layer of the protrusion 14. Accordingly, the protrusion 14 may have substantially the same multilayer structure, except for the insulating layer 20 as the infrared laser element 13. The protrusion 14 is not used for emitting a laser. This is because the protrusion 14 does not have a p-side electrode. Instead of the p-side electrode, the protrusion 14 has the insulating layer 20. In other words, the protrusion is dummy laser element. One example for the insulating layer is SiO2. Alternatively, the protrusion may have less layers and not include all layers that would make it a laser element but for the lack of the p-side electrode.
The height of the protrusion 14 from the substrate 11 may be substantially equal to the height of the visible laser element 12 and infrared laser element 13.
The top surface of the protrusion 14, the top surface of the visible laser element 12, and the top surface of the infrared laser 13 may be substantially in the same plane.
The detail structure of semiconductor laser array 10 of this embodiment is explained with reference to
As shown in
A multilayer structure of the visible laser element 12 is explained hereinafter. As shown in
InGaAlP cladding layer 46 are formed on the substrate 11 in this order. The active layer 44 may be a MQW (Multi-Quantum Well) of In0.5Ga0.5P/In0.5(Ga0.5Al0.5)P0.5.
A p-type In0.5Ga0.5P etching stop layer 50 is provided on the first p-type cladding layer 46. A second p-type InGaAlP cladding layer 51 and a p-type cap layer 52 are formed as a ridge stripe waveguide structure 53 on the etching stop layer 50.
A n-type InAlP current block layer 76 is provided on the p-type In0.5Ga0.5P etching stop layer 50, a side of the second p-type InGaAlP cladding layer 51 and a side of the cap layer 52. In other words, the current block layer 76 is provided except for ridge stripe waveguide structure 53.
A p-type contact layer 78 is provided on the current block layer 76 and the cap layer 52. A top surface of the contact layer 78 is flat. A p-side electrode 18 is provided on the contact layer 78.
A structure of the infrared laser element 13 is explained hereinafter.
As shown in
A p-type InGaP etching stop layer 70 is provided on the first p-type cladding layer 66. A second p-type InGaAlP cladding layer 71 and a p-type cap layer 72 are formed as a ridge stripe waveguide structure 73 on the etching stop layer 70.
The n-type InAlP current block layer 76 is provided on the p-type InGaP etching stop layer 70, a side of the second p-type InGaAlP cladding layer 71 and a side of the low resistance 72. In other words, the current block layer 76 may be provided except for the ridge stripe waveguide structure 73.
A p-type contact layer 78 is provided on the current block layer 76 and the cap layer 72. A top surface of the contact layer 78 is flat. A p-side electrode 19 may be provided on the contact layer 78.
The n-side electrode 17 is provided on the back surface of the substrate 11.
As mentioned above, the visible laser element 12 and the infrared laser element 13 (which emits different wavelength laser) are provided on one substrate. The cavity lengths of resonator L1 and L2 are capable of being set independently in order to reduce the threshold current and the power consumption.
The structure of the protrusion 14 is explained hereinafter. The protrusion 14 has the same layer structure except for the insulating layer 20 as the infrared laser element 13. On the substrate 11 the n-type GaAs buffer layer 61, the n-type InGaAlP cladding layer 62, the GaAlAs active layer 64, the first p-type InGaAlP cladding layer 66, the p-type InGaP etching stop layer 70, the second p-type InGaAlP cladding layer 71 and the p-type cap layer 72, the n-type InAlP current block layer 76 and the p-type contact layer 78 are formed.
On the above mentioned layer structure, the insulating layer 20 is provided on the contact layer 78. The insulating layer 20 makes the protrusion not to injected current into and not to use for emitting laser.
A metal such as the same material as the p-side electrodes 18, 19 may be provided between the top surface of the contact layer 78 and the insulating layer 20. This also prevents the current from being injected into protrusion 14.
The manufacturing process of the semiconductor laser array 10 is explained with reference to
As shown in
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The process for manufacturing the trench 16 (which separates the infrared laser element 13 and the protrusion 14) is explained hereinafter.
As shown in
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Furthermore the substrate 11 is polished to be thick. The n-side electrode 17 is formed on the back surface of the substrate 11. The p-side electrodes 18, 19 are annealed to be alloy.
Furthermore, the cleavage process is operated. So the semiconductor laser array 10 as shown in
In this embodiment, the trench 16 is formed after the trench 15 is formed. But the trench 16 may be formed at the same manufacturing step of forming trench 15 or formed before trench 15 is formed.
In case that the distance L3 between the emitting center of the laser between the laser element 12 and 13 is 110 micrometers, the cavity length of resonator L1, L2 may be 1500 micrometers and the light output of the laser element 13 may be 7 mW, the power consumption of laser element 12 and 13 is 140 mW, respectively. In a single infrared laser element, in case that the cavity length of the laser element is 400 micrometers and the light output of the laser element is 7 mW, the power consumption of laser element is 70 mW. Namely the shorter cavity length of resonator is preferable for reducing the power consumption.
As shown in
The semiconductor laser array 10 may eventually be mounted on submount 104. The submount 104 is fixed to the stem 102. The four leads 101 are extended from the stem 102 to the opposite direction of the main emitting direction of the semiconductor laser array 10.
The photodiode (PD) 103 that is for monitoring laser from the semiconductor laser array 10 are mounted on the stem 102. The monitoring laser received by the PD 103 is used for controlling the semiconductor laser array 10.
The metal cap 105 is enclosure of semiconductor laser array 10 and PD 103 and fixed to the stem 102.
The window 106 is provided on the metal cap 105 and a visible laser 107 and an infrared laser 108 are emitted from the window 106 toward outside of the multiple wavelength laser device 100.
As shown in
In this case, the protrusion 14 is contact with the submount 104 without an adhesive. So the top face of the semiconductor laser array 10, that is p-side electrodes 18, 19 and insulating layer 20,
In this embodiment, the protrusion is provided on the substrate. The protrusion supports the submount. The protrusion disperses the stress on the semiconductor laser array to the visible laser element, the infrared laser element and itself more evenly.
In case the height of the protrusion is equal to that of the visible laser element or the infrared laser element, the stress is reduced more. It is preferable that the top face of the protrusion, the visible laser element and the infrared laser element is substantially flat.
In this embodiment, it is available that the cavity length of the resonator of the visible laser element and the infrared laser element is set independently. The threshold current of the infrared laser is reduced.
An interposer such as insulating material or a metal may be provided between the protrusion 14 and the submount 104. It is preferable that the thickness of the interposer is substantially equal to that of the solder. This make the contact area between the semiconductor laser array 10 and the submount 104 increased. So the stress on the semiconductor laser array 10 is dispersed more. That is the stress distribution is increased.
In this second embodiment, a part of the protrusion 14 is slanted against the rear end face 85 of the infrared laser element 13.
As shown in
The laser “a” as illustrated in
It is preferable that an angle between the slanted face 121 and the rear end face 85 is 0-45 degree. But the angle is not limited to this range. The angle is set so as to reduce the optical feed back.
For example, a slanted face of the protrusion may be toward in-side as shown in
The laser “b” as illustrated in
Furthermore, a slanted face of the protrusion may be toward up-side as shown in
The laser “c” as illustrated in
The slanted face 121 and 131 are formed by forming the photo resist mask 83 slanted in the manufacturing process as shown in
In this third embodiment, a semiconductor laser device 200 has a diffraction grating (hologram) 201. The diffraction grating 201 is a hologram.
As shown in
As shown in
An operation of the semiconductor laser device of this embodiment is explained hereinafter.
As shown in
As shown in
The visible laser element 12 is operated for reading data recorded in DVD medium. The infrared laser element 13 is operated for reading data recorded in CD medium.
Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and example embodiments be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following.
The way semiconductor laser array mounted on the submount is not limited to junction down. The semiconductor laser array may be mounted on the submount with junction up (upside up).
Semiconductor laser elements are not limited to GaAlAs, InGaAlP, and GaN lasers. Other semiconductor laser elements are available such as by using a Ill-V compound semiconductor, II-VI compound semiconductor, and so on.
Other embodiment of the present invention may be possible by changing the shape, size, material, and positional relations in design by one skilled in the art.
Number | Date | Country | Kind |
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2004-278289 | Sep 2004 | JP | national |