SE531622C2 - Modulator with angled waveguides for phase modulation - Google Patents

Description

30 531 E22 is applied to the waveguide. Conversely, the change in real index due to the LEO will be added to the quadratic electro-optical effect of TE-polarized light if the waveguide is in the v-groove direction.

Similarly, a substrate of InP or GaAs and having a crystal growth direction, specified by Milleríndex, will show an addition of the index change due to the LEO and quadratic electro-optical effects of TE-polarized light in a waveguide located in the direction and to show competition between the two effects if the waveguide is oriented in the direction.

The competition between the LEO effect and other effects used to change the refractive index leads to a reduced ability to achieve phase modulation for a waveguide, which is placed after a laser in an integrated optical circuit with essentially the same orientation as the laser in relation to the crystal axes.

The manufacturing processes that define the laser waveguide are dependent on the crystal direction and these have reached a technical maturity in the sense that it is now possible to manufacture very reliable lasers in this crystal direction, so it would be advantageous to still be able to manufacture lasers in this direction without disadvantages. performance due to dependencies of the LEO direction when a phase modulator is connected.

The present invention makes this possible.

Thus, the present invention relates to a waveguide in a phase modulator for laser light which is monolithically integrated with a laser which is arranged to produce said light and in which the laser has a waveguide which is oriented so that it can emit light in a crystal direction, in which the linear electro-optical power (LEO), which is used to change the refractive index sign of TE-polarized light in a waveguide in a modulator, competes with one or more other physical effects , which is used to change the sign of refractive index in the modulator, such as Kerr or quadratic electro-optical effect and is characterized in that said monolithically integrated waveguide in a modulator is oriented in a direction which is not parallel to the direction in which the laser waveguide is oriented.

In the following, the present invention is described in more detail, partly in connection with exemplary embodiments of the invention and a drawing, in which Figure 1 shows a first embodiment of the present invention - Figure 2 shows a second embodiment of the present invention - Figure 3 shows a third Embodiment of the present invention - Figure 4 shows a fourth embodiment of the present invention - Figure 5 shows a fifth embodiment of the present invention - Figure 6 shows a sixth embodiment of the present invention - Figure 7 shows a seventh embodiment of the present invention. Figure 1 shows a waveguide in a phase modulator 1 for laser light, which is monolithically integrated with a laser 2 for generating said light on a substrate 3.

The laser 2 has a waveguide 4, which is oriented to emit light in a crystal direction where the linear electro-optical effect (LEO), which is used to change the refractive index sign of TE-polarized light in a modulator waveguide, competes with one or more other physical effects used to change the refractive index sign in the modulator, such as the Kerr or quadratic optical effect.

According to the invention, said monolithically integrated waveguide in the modulator 1 is oriented in a direction which is not parallel to the direction in which the waveguide 4 of the laser 2 is oriented. The modulator 1 has two parallel waveguide arms 5, 6, each of which is provided with a metal electrode. One or both of said electrodes are connected to a voltage source which is arranged to apply a bias voltage and a modulation voltage.

Thus, the modulator waveguide is oriented in a direction in which the competition between the LEO effect and one or more other physical effects used to change the refractive index sign in the modulator decreases, or where LEO is an additive relative to one or more effects.

In all embodiments described in this patent application, the modulator may include quantum wells.

According to a preferred embodiment, the waveguide arms 5, 6 of the modulator are rectilinear and oriented in a direction, 10 22 20 25 30 53fi G22 which is at an angle of between 20 and 90 degrees in relation to the direction in which the laser waveguide is oriented - rad.

In Figure 1, the modulator arms 5, 6 are oriented in a direction perpendicular to the laser waveguide 4. An Au-coated, 45 degree angled mirror 18, 19 is arranged in each arm 5, 6. Each of the modulator arms 5, 6 is provided with metal electrodes 7, 8, which are connected to terminals 9, 10 for applying a voltage to the electrodes, whereby the refractive index is changed to achieve optical modulation.

This embodiment provides a full LEO effect.

In Figure 2, the modulator arms 5, 6 form an angle of approximately 45 degrees with respect to the waveguide 4 of the laser, not shown in Figure 2. This embodiment gives no LEO effect and is the most preferred embodiment. This embodiment does not require mirrors.

The laser 2 is shown only in Figure 1. Figure 3 shows another preferred embodiment, where each arm 11, 12 of the modulator 1 comprises at least one curved section, where the tangent of the curve in at least a part of the curved modulator waveguide forms an angle of at least 20 degrees in relation to the direction in which the laser guide 4 is oriented. This embodiment requires no mirrors and makes it possible to manufacture a narrow chip.

Figure 4 illustrates a further embodiment, where each arm 13, 14 nose modulator comprises at least two rectilinear sections 13a, 13b; 14a, 14b, each section 13a, 13b; 10 15 20 25 30 531 B22 14a, 14b in each arm 13, 14 form an angle of between 20 and 90 degrees relative to each other. At least a section of the modulation arm is oriented in a direction substantially between 20 and 90 degrees relative to the direction in which the waveguide 4 of the laser is oriented. In this embodiment, an integrated mirror 15, 16 is arranged at the transition between the respective modulator sections 13a, 13b; l4a, 14b.

This embodiment also eliminates the LEO effect in the specific fall when the sections are oriented 45 degrees in relation to the orientation of the laser waveguide. The advantage over the embodiment shown in Figure 2 is that it is possible to manufacture a narrower chip.

In accordance with a modified embodiment, compared to the arrangement shown in Figure 4, each arm 13, 14 of the modulator comprises at least two rectilinear sections 13a, 13b; 14a, 14b, where each section forms an angle of between 20 and 90 degrees relative to each other and where at least one section 13a, 13b; 14a, 14b of each arm 13, 14 are oriented in a direction substantially between 20 and 90 degrees in relation to the direction in which the waveguide 4 of the laser is oriented. However, in accordance with this modified embodiment, one or more curved waveguide sections 13c; 14c arranged between the respective rectilinear modulator sections 13a, 13b; l4a, l4b, see figure 5.

Figure 6 shows a modulator, where the arms 13, 14 are directed perpendicular to the laser waveguide 4, but where the waveguide 4 of the laser and the output waveguide 17 of the modulator 1 are parallel. This embodiment provides full LEO effect. In accordance with a further preferred embodiment, which is shown in Figures 7, 21, 2la, the modulator 1 comprises two arms 20, each arm consisting of two modulation sections 20a, 20b, 2lb, where a first modulation section 20a in an arm 20 is oriented substantially in the same direction as the laser guide 4 and where the second modulation section 20b of said arm is oriented at an angle of substantially 90 degrees relative to the direction of the laser guide 4 and where the first modulation section 21a of the second arm 21 is oriented at an angle of substantially 90 degrees relative to the waveguide 4 of the laser and the second modulation section 21b of this arm is oriented substantially in the same direction as the waveguide 4 of the laser. In accordance with this embodiment the first sections 20a, 21a of each respective arm have electrodes 22, 23 which are electrically connected to each other and the second sections 20b, 21b of each respective arm have electrodes electrodes 24, 25, which are electrically connected to each other. The electrodes are connected to sockets 26, 27. Mirrors 26, 27 or curved sections are arranged in the transition between the modulation sections.

In accordance with a preferred embodiment, the connected arm pairs are 22, 23; 24, 25 connected to a voltage source, which is not shown and which is arranged to apply a voltage to each of the two respective arm pairs according to a biased push-pull modulation scheme, see figure 7.

In the embodiment shown in Figure 7, the LEO is the primary source for achieving a refractive index change. This configuration is particularly advantageous in a push-pull modulation mode, since the absorption due to the oscillation in modulation voltage will be substantially balanced. in the two arms over an entire cycle of the modulation voltage oscillation, so that the quench ratio at the output of the modulator is expected to be excellent, without the need for asymmetric splitting or other methods to improve the quench ratio.

With the modulators described above in Figures 1 to 6, the amplitude of the applied voltage required to achieve any specific phase modulation magnitude is reduced compared to modulators where the phase modulator waveguide is substantially parallel to the laser waveguide oriented along the traditional crystal direction. used to define such waveguides.

The reduced need for voltage amplitude oscillation enables the achievement of optical modulation by means of HF circuits, which emit a smaller power than in the case where the methods described herein are not used.

The reduced modulation voltages also mean a reduction in unwanted absorption losses, since such losses tend to increase monotonically with the depth of the voltage modulation.

For the specific case of 45 degree orientation of the waveguide, as shown in Figure 2, the linear electro-optical power (LEO) is completely eliminated.

It is obvious that the embodiments described above can be modified without departing from the spirit of the invention as expressed in claim 1.

Therefore, the invention is not limited to the above-described embodiments of the invention, but may be modified within the scope of the claims.

Claims (11)

10 15 20 25 30 53 'I B22 Patent claims A waveguide in a phase modulator (1) for laser light, which is monolithically integrated with a laser (2,) which is arranged to produce said light and wherein the laser (2) has a waveguide (4), which is oriented so that it can emit light in a crystal direction, in which the linear electro-optical power (LEO), which is used to change the refractive index sign of TE-polarized light in a waveguide in a modulator (1), competes with one or more several other physical effects used to change the refractive index sign in the modulator (1) I such as Kerr or quadratic electro-optical effect, characterized by said monolithic integrated guides (5,6; 10, 11; 13, 14, 14) 20,2l) in a modulator (1) is oriented in a direction which is not parallel to the direction in which the laser waveguide (4) is oriented. A phase modulator according to claim 1, characterized in that the modulator (1) has two parallel waveguide arms (7, 8; 10, 11: 13, 14; 20.2l), electrode (7.8; 22-25). each of which is provided with a metal A phase modulator according to claim 2, characterized in (5,6) that the waveguide arms of the modulator (1) are rectilinear and oriented in a direction with an angle of between 20 and 90 degrees relative to the direction in which 1a - the power guide (4) is oriented. A phase modulator according to claim 2 or 3, characterized (13, 14) at least two rectilinear sections (13a, 13b, 14a, 14b), wherein each arm of the modulator comprises each section of each arm forming an angle of between 20 and 90 degrees relative to each other and of at least one section (13a, 13b, 14a, 14b) of each arm being oriented in a direction substantially between 20 and 90 degrees from the direction in which the laser waveguide (4) is oriented and in that an integrated mirror (15, 16) is arranged at the transition between the respective modulator sections (13a, 13b, 14a, 14b). A phase modulator according to claim 2 or 3, characterized in that each arm (l3, l4) of the modulator (l) comprises at least two rectilinear sections (l3a, l3b, l4a, l4b), each section forming a angle of between 20 and 90 degrees relative to each other, in that at least one section (13a, 13b, 14a, 14b) in each arm is oriented in a direction substantially between 20 and 90 degrees from the direction in which the laser waveguide ( 4) is oriented and in that one or more curved waveguide sections (13c, 14c) are arranged between the respective rectilinear modulator sections (13a, 13b, 14a, 14b). A phase modulator according to claim 2 or 3, characterized in that the modulator (1) is oriented in a direction substantially 90 degrees from the direction in which the laser waveguide (4) is oriented. A phase modulator according to claim 2, characterized (l1, l2) at least one curved section (ll, l2), wherein the tangent of the curve in that each arm of the modulator (1) comprises at least one piece of the curved modulator waveguide forms an angle of at least 20 degrees with respect to the direction in which the laser waveguide (4) is oriented. A phase modulator according to claim 2, characterized in that the modulator comprises two arms, each arm consisting of two modulator sections, in that a first modulation section (20a) in an arm (20) is oriented in substantially the same direction. 531 E22 in the direction of the laser waveguide (4) and wherein the second modulation section (20b) of said first arm is oriented at an angle of substantially 90 degrees relative to the direction of the laser waveguide (4), in that the first the modulation section (2la) (21) with an angle of substantially 90 degrees relative to the second arm is oriented the laser guide guide (4), in that the second modulation section (2lb) of this arm is oriented in substantially the same direction as the laser waveguide (4), in that the first sections (20a, 2la) of each respective arm are electrically connected to each other and where the second sections (2la, 2lb) of each respective arm are electrically connected to each other. A phase modulator according to claim 8, characterized in that the interconnected arm pairs (20a, 2la; 20a, 2lb) are connected to a voltage source, which is arranged to apply a voltage to each of the two respective arm pairs. a push-pull modulation scheme. A phase modulator according to any one of the preceding claims, characterized in that the modulator (1) comprises quantum wells. 11. ll. A phase modulator according to any one of the preceding claims, characterized in (7,8; 22-25) that one or both of said electrodes are connected to a voltage source, which is arranged to apply a direct bias voltage alone or in combination with a signal modulation voltage.