EP1358701A2

EP1358701A2 - Laser structure and method for adjusting a defined wavelength

Info

Publication number: EP1358701A2
Application number: EP02706629A
Authority: EP
Inventors: Bernhard STEGMÜLLER
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies AG
Priority date: 2001-02-08
Filing date: 2002-01-25
Publication date: 2003-11-05
Also published as: KR20030077016A; DE10105731A1; WO2002063732A2; US20040114658A1; TW522620B; JP2004525507A; WO2002063732A3

Abstract

The invention relates to a laser structure on a semiconductor substrate, comprising a first resonator, a second resonator and a third resonator. The second resonator and the third resonator are configured as ring resonators and are arranged in at least one common section next to the first resonator and next to the second resonator, respectively, at a substantially constant distance to the first resonator and the second resonator, respectively. The second resonator is thereby optically coupled to the first resonator and the third resonator via the second resonator or directly to the first resonator in such a manner that a stationary wave having a defined wavelength can be produced in the first resonator.

Description

Besehreibung

Laser structure and method for setting a defined wavelength

The invention relates to a laser structure and a method for setting a defined wavelength.

A laser diode with adjustable narrow-band emission wavelength is a key component in optical signal transmission and signal processing technology. The setting of a defined emission wavelength and the coupling of different signals with different wavelengths (so-called carrier frequencies) is necessary in order to be able to achieve an extremely high data transmission rate of more than 1 TBit / s.

A laser diode is known in which the wavelength selection is carried out with the aid of a distributed feedback or distributed Bragg reflector structure. With such a structure, a light wave is generated and guided in a light-guiding strip or film, which is also the active area. The guidance along the film is effected by differences in refractive index between the core area and the cladding area. Through periodic

Varying the thickness of the core region results in light scattering and interference in part of the generated wavelengths in accordance with the Bragg condition.

In the case of a distributed Bragg reflector structure, the periodic variation in the core region thickness at the end regions of the active optical film is used instead of resonator mirrors, as a result of which light of a specific wavelength can be specifically selected by reflection and then amplified. In the case of a distributed feedback structure, on the other hand, the periodic variation in the core region thickness is spread along the entire active optical film, as a result of which optical excitation takes place only at a specific wavelength.

The setting of the laser wavelength is usually done by tuning the resonance wavelength in the laser resonator through physical action. For example, the resonance wavelength can be influenced by means of the current flow through the active optical film, by means of the voltage applied to the active optical film or by means of the temperature prevailing in the active optical film.

Alternatively, the laser wavelength can be set by optically coupling various linear individual resonators, so that certain wavelengths are preferred. The best-known linear individual resonators are the Fabry-Perot resonator, the distributed feedback resonator and the distributed Bragg reflector resonator. The distributed Bragg reflector resonator is a resonator with parallel resonator mirrors, which is used above all in surface-emitting lasers (VCSEL = vertical cavity surface emitting laser), the resonator mirrors being arranged on the end faces of the VCSEL substrate.

Due to a relatively weak optical coupling between the linear individual resonators, it is necessary that the dimensions of the optical components with the linear individual resonators be several 100 μm. This is especially the case when the wave propagation takes place in the plane of the grown epitaxial layers with which the optical components are produced.

From JP 04349682 A a light source for optical communication is known which can control a high light output power over a wide frequency range or is operated over a wide range of optical output power on a single wavelength, using a semiconductor laser with coupled modes. A first semiconductor laser section is optically coupled to a second semiconductor laser section by means of a resonator, the first semiconductor laser section being operated with high output power and the second semiconductor laser section being operated at a single wavelength. A DFB (distribution feedback) ring laser can be used as the second semiconductor laser section. The two semiconductor laser sections represent two separate individual resonators.

In Opt. Lett., Vol. 22, No. 16, pp. 1244 - 1246 (1997), two waveguides are optically coupled to one another by means of a ring or disk resonator. The ring or disc resonator takes on the function of a switching element, which can be used to control whether a light signal carried in one waveguide is also transmitted by means of the other waveguide. However, there is no variable setting of a narrow-band emission wavelength. To produce a ring resonator, Appl. Phys. Lett., Vol. 66, No. 20, pp. 2608-2610 (1995).

A combination of optically coupled individual resonators with a physical effect on the resonance frequency of the separate individual resonators enables a narrow-band emission wavelength, but leads to this

2 a large component size of up to several 0.01 mm.

In addition, the production of separate individual resonators is very complex and therefore expensive. In the case of the distributed feedback resonator and the distributed Bragg reflector resonator, this is due to the difficult periodic variation in the core region thickness and, in the case of the Fabry-Perot resonator, the difficult production of optically highly reflective, parallel mirrors at the resonator ends. The invention is therefore based on the problem of specifying a laser structure and a method for setting a defined wavelength, with which compared to the described prior art, despite the lower

Component size a narrow-band emission wavelength can be achieved.

The problem is solved by a laser structure and by a method for setting a defined wavelength with the features according to the independent patent claims.

A laser structure on a semiconductor substrate has a first resonator, a second resonator and a third resonator. The second resonator and the third resonator are designed as ring resonators and are arranged in at least one common section next to the first resonator or next to the second resonator, essentially at a constant distance from the first resonator or second resonator. This makes the second

Resonator optically coupled to the first resonator and the third resonator via the second resonator or directly to the first resonator such that a standing wave with a defined wavelength can form in the first resonator.

The common section, in which a resonator is arranged next to another resonator at a substantially constant distance from the other resonator, has a length of at least several wavelengths of the emitted

Laser radiation on so that a sufficient overlap of the optical wave functions of the two resonance waves is guaranteed. This overlap influences the resonance frequencies of the two resonators and thus enables the setting of the emitted laser radiation. The following steps are carried out in a method for setting a defined wavelength: A first resonator is provided in a laser structure on a semiconductor substrate. A ring resonator is arranged as a second resonator in at least one common section next to the first resonator at a substantially constant distance from the first resonator. Another ring resonator is arranged as a third resonator in at least one common section next to the second resonator or next to the first resonator, essentially at a constant distance from the second resonator or first resonator. The second resonator is optically coupled to the first resonator and the third resonator is optically coupled via the second resonator or directly to the first resonator in such a way that a standing wave with a defined wavelength can form in the first resonator.

An advantage of the invention is that the laser structure according to the invention has a component size of a few 100 μm 2,

2 preferably has a maximum component size of 100 μm, the actual component size being different from that

Number of resonators depends on the desired wavelength and on the component materials used. The laser structure according to the invention is thus suitable for use in a highly integrated circuit (VLSI circuit = very large scale

Integration).

Another advantage of the invention results from the use of ring resonators of different sizes by nesting them together, which enables optical coupling of the resonators in a very small space and thus a further reduction in component size. With optical coupling of resonators whose resonance wavelengths differ by only a few percent, the desired emission wavelength can also be set on the basis of the vernier effect respectively. Depending on the desired emission wavelength, more or fewer resonators are then optically coupled to one another by further resonators acting as switching elements.

Finally, there is a further advantage that the use of pure ring resonators in the invention reduces the manufacturing effort for the resonators. This is due to the fact that dispensing with distributed feedback and distributed Bragg reflector resonators means that there are no difficult periodic variations in the core area thickness and that dispensing with Fabry-Perot resonators means that no optically highly reflective, parallel mirrors have to be produced at the resonator ends , As a result, the manufacturing costs for the optical component are consequently significantly reduced.

The laser structure according to the invention is preferably set up in such a way that the third resonator and the second resonator are nested in one plane. For example, the second resonator and the third resonator can be arranged in a first plane, while the first resonator is arranged in a plane parallel to the first plane. Alternatively, the third resonator and the second resonator can also be arranged next to one another in parallel planes.

The laser structure according to the invention is preferably set up in such a way that the respective optical coupling of the three resonators can be changed by at least one external parameter. A laser structure provided in this way enables the user to be able to influence the defined wavelength in the first resonator. Depending on the external parameter, the resonance frequency of the second resonator and the third resonator can be set variably. By optically coupling the second resonator and the third resonator to the first resonator, a defined laser wavelength can be set in the first resonator.

The group of external parameters preferably includes the current flow, the temperature and the applied voltage.

In a preferred development of the laser structure according to the invention, at least one further ring resonator is optically coupled to the first resonator directly or via one of the other resonators. The direct or indirect optical coupling of further resonators to the first resonator makes it possible to achieve a higher accuracy when setting the defined laser wavelength in the first resonator.

In a further preferred development of the laser structure according to the invention, at least one further resonator is arranged adjacent to the three resonators. The further resonator enables control of the respective optical coupling between the individual resonators.

For example, the further resonator can be used as a switching element which can switch the optical coupling between the first resonator and the second resonator on and off and thus influences the setting of the defined laser wavelength in the first resonator.

The laser structure according to the invention is preferably set up in such a way that the second resonator, the third resonator and each further ring resonator each act as a wavelength filter on the first resonator.

In the laser structure according to the invention, the second resonator, the third resonator and each further resonator are preferably each designed as a distributed feedback resonator or as a distributed Bragg reflector resonator. do

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Ring resonators are particularly suitable. Circles, ellipses and polygons, for example, are possible as shapes for ring resonators, each of which is arranged adjacent to one another in a plane and nested with different sizes. The geometric shape is the

Ring resonators only secondary, as long as each resonator has the shape of a closed ring.

A three-dimensional arrangement of the resonators is also possible, i.e. some resonators are arranged adjacent within a plane, while in a parallel plane further resonators are arranged adjacent, which can also be formed concentrically to the adjacent resonators. Given the same spacing of the resonators, an optical coupling of resonators in parallel planes is for epitaxial reasons at least a factor 10 better than an optical coupling of resonators within one plane.

Embodiments of the invention are shown in the figures and are explained in more detail below. The same reference numerals designate the same components.

FIG. 1 shows a top view of a laser structure according to a first exemplary embodiment of the invention;

FIG. 2 shows a cross section through the laser structure from FIG. 1 along the section line A-A;

Figure 3 is a plan view of a laser structure according to a second embodiment of the invention;

Figure 4 is a plan view of a laser structure according to a third embodiment of the invention; and

Figure 5 shows a cross section through the laser structure of Figure 4 along the section line BB.

optically primarily with the surrounding second ring resonator 130.

Furthermore, there are two first ones in the area of the laser structure 100 enclosed by the first ring resonator 120

Control resonators 150 and four second control resonators 160, each with an electrical contact 121, are arranged such that the optical coupling of the individual ring resonators to one another can be switched on and off. An exact setting of the resonance frequency in the first ring resonator 120 and consequently a narrow-band emission wavelength for the entire laser structure 100 is thus possible.

To illustrate the arrangement of the laser structure 100, FIG. 2 shows a cross section 200 through the laser structure 100 shown in FIG. 1 along the section line A-A. In cross section 200 it becomes clear that the laser structure 100 is based on a substrate 201.

Furthermore, a cross section through the active resonator region 111 of the Fabry-Perot resonator 110 and through the first ring resonator 120 is shown. The two resonators are arranged in a plane parallel to and through the surface of the substrate 201

Insulation material 202 electrically insulated from one another and from the environment. A dielectric material can be selected as the insulation material 202. Alternatively, the insulation material 202 can also be dispensed with entirely, which is why the insulation is then to be accomplished by air.

The two resonators are supplied with electrical energy by the electrical contacts 113 and 121, the resonators being transversely flowed through by the electrical energy flow 203. The two resonators shown have a width of up to 20 μm and a distance of up to 5 μm from one another. The optical coupling of the resonators takes place on the basis of an optical overlap of the two resonance wavelengths, which enables an optical energy flow 204 between the two resonators.

3 shows a top view of a laser structure 300 according to a second exemplary embodiment of the invention.

In contrast to the laser structure 100 according to the first

Exemplary embodiment of the invention, the laser light is emitted by a curved resonator 310 with an active resonator region 311, resonator mirrors 312 and an electrical contact 313.

Second ring resonators 330 of smaller size are arranged within the first ring resonator 320, a third ring resonator 340 being nested in one of the second ring resonators 330.

In order to provide an optical coupling possibility between the first ring resonator 320, the second ring resonators 330 and the third ring resonator 340 and above all to the curved resonator 310, the ring resonators in this exemplary embodiment have an elliptical shape. The ring resonators are thus arranged next to one another and to the curved resonator 310, at least in a common section, essentially at a constant distance from one another.

The laser structure 300 according to the second exemplary embodiment has a small space requirement on a semiconductor substrate due to the nesting of the ring resonators, just like the laser structure 100 according to the first exemplary embodiment. 4 shows a top view of a laser structure 400 according to a third exemplary embodiment of the invention.

The components already described in FIG. 1 are not discussed again here.

The laser structure 400 of this exemplary embodiment differs from the laser structure 100 according to the first

Exemplary embodiment by the following features: The first ring resonator 410 with the nested second ring resonators 420 is arranged in a plane adjacent to the plane of the Fabry-Perot resonator 110. For an explanation, reference is made to FIG. 5. β In addition to the first ring resonator 410, a group of nested third ring resonators 430 and a group of nested fourth ring resonators 440 are optically coupled directly to the Fabry-Perot resonator 110.

The second ring resonators 420, the third ring resonators 430 and the fourth ring resonators 440 have the shape of hexagons.

FIG. 5 shows a cross section 500 through the laser structure 400 shown in FIG. 4 along the section line B-B. In this illustration, the arrangement of the resonators in several planes is particularly clear.

The components already described in the previous figures are not discussed again here.

The arrangement of the resonators in a plurality of parallel planes on the one hand results in an optical coupling of the resonators within one plane, which enables a horizontal optical energy flow 501 between the first ring resonator 410 and the second ring resonators 420, and on the other hand an optical coupling of the resonators between adjacent ones Levels, creating a vertical optical Energy flow 502 between the active resonator region 111 of the Fabry-Perot resonator 110 and the first ring resonator 410 is made possible.

The emitted laser wavelength thus results from a mixture of the individual optical couplings to the emitting resonator, ie a multiple overlap of the optical wave functions of the resonance waves of the different resonators.

LIST OF REFERENCE NUMBERS

100 laser structure according to the first embodiment

110 Fabry-Perot resonator

111 active resonator area

112 resonator mirrors

113 electrical contact

120 first ring resonator

121 electrical contact 130 second ring resonators 140 third ring resonators 150 first switching resonator 160 second switching resonators

200 cross section through laser structure 100 along A-A

201 substrate

202 insulation material

203 electrical energy flow

204 optical energy flow

300 laser structure according to the second embodiment

310 curved resonator

311 active resonator area

312 resonator mirror

313 electrical contact 320 first ring resonator 330 second ring resonators 340 third ring resonator

400 laser structure according to the third embodiment

410 first ring resonator

420 second ring resonators

430 third ring resonators

440 fourth ring resonators

500 cross section through laser structure 400 along B-B

501 horizontal optical energy flow

502 vertical optical energy flow

Claims

claims

1. laser structure on a semiconductor substrate,

With a first resonator, a second resonator and a third resonator,

In which the second resonator and the third resonator are designed as ring resonators,

In which the second resonator is arranged in at least one common section next to the first resonator at a substantially constant distance from the first resonator, and

In which the third resonator is arranged in at least one common section next to the second resonator or next to the first resonator at a substantially constant distance from the second resonator or first resonator,

• whereby the second resonator is optically coupled to the first resonator and the third resonator via the second resonator or directly to the first resonator such that there is a standing one in the first resonator

Can form a wave with a defined wavelength.

2. Laser structure according to claim 1, in which the third resonator and the second resonator are arranged nested in one plane.

3. Laser structure according to claim 1, in which the third resonator and the second resonator are arranged side by side in parallel planes.

4. Laser structure according to claim 2, in which the second resonator and the third resonator are arranged in a first plane and in which the first resonator is arranged in a plane parallel to the first plane.

5. Laser structure according to one of claims 1 to 4, in which the respective optical coupling of the three resonators can be changed by at least one external parameter, as a result of which influence can be exerted on the defined wavelength in the first resonator.

6. Laser structure according to claim 5, in which the group of external parameters includes the current flow, the temperature and the applied voltage.

7. Laser structure according to one of claims 1 to 6, in which at least one further ring resonator is optically coupled to the first resonator directly or via one of the other resonators.

8. Laser structure according to one of claims 1 to 7, in which at least one further resonator is arranged adjacent to the three resonators, which enables control of the respective optical coupling between the three resonators.

9. Laser structure according to one of claims 1 to 8, in which the second resonator, the third resonator and each further ring resonator are each set up to act as a wavelength filter on the first resonator.

10. Laser structure according to one of claims 1 to 9, in which the second resonator, the third resonator and each further resonator are each designed as a distributed feedback resonator or as a distributed Bragg reflector resonator.

11. Method for setting a defined wavelength with the following steps: providing a first resonator in a laser structure on a semiconductor substrate, Arranging a ring resonator as a second resonator in at least one common section next to the first resonator at a substantially constant distance from the first resonator, arranging a further ring resonator as a third

Resonator in at least one common section next to the second resonator or next to the first resonator, essentially at a constant distance from the second resonator or first resonator, and • optically coupling the second resonator to the first resonator and the third resonator via the second Resonator or directly to the first resonator such that a standing wave with a defined wavelength can form in the first resonator.