FR2840689A1 - Integrated optical waveguide having channel/optical substrate and guide layer having index above substrate and waveguide having adaptation layer extending either side channel. - Google Patents

Abstract

The optical waveguide has a channel (12) on an optical substrate (11). The refractive index of the channel is higher than that of the substrate. There is a guide layer (15) on the channel with an index higher than the substrate. The waveguide has an adaptation layer (13,14) extending on either side of the channel.

Description

has a spacer no.4 support for the adjustment arm no.4 this spacer

is articulated in rotation.

  t Waveguide comprising a channel and an adaptation layer The present invention relates to a waveguide comprising a channel and

an adaptation layer.

  The field of the invention is that of integrated optical devices on a substrate, a field in which an essential element is the waveguide which performs the function of transporting the light energy necessary for the routing of an optical signal. With reference to patent application FR 2 818 390, such a guide is produced by creating a channel by ion implantation of the substrate through a mask, then by depositing a guiding layer.

o on the canal.

  The guide not being limited to the single channel but rather constituted by the association of this channel and the guiding layer, it then has dimensions in adequacy with that of the core of an optical fiber. Indeed, the

  integrated devices are often interconnected with optical fibers.

  The geometrical structure of the guide means that it is likely to

  exhibit behavior that differs depending on the state of polarization of the light.

  This sensitivity to polarization is all the stronger the higher the implantation dose. The difference between the effective indices of refraction in transverse electrical mode (TE) and in transverse magnetic mode (TM) increases to

  as the channel refraction index increases.

  The sensitivity to polarization is a critical parameter for any device connected to an optical fiber. Indeed, when the fiber is stressed, in particular when it is bent, this curvature leads to a modification of the polarization of the light which circulates there. It is therefore not possible to know the state of polarization of the light entering the device. It follows that this it is necessary to present a sensitivity to the polarization that is most redu ite.

  possible so that the integrity of the optical signal is best preserved.

  In particular, the radiative losses in the bends depend on the contrast of lateral index ANeff, contrast which is defined as the difference between the effective index of refraction defined at the level of the channel and that defined outside this channel. This contrast itself depends on the polarization mode. It is desirable that the ANeffTE lateral contrast in TE mode is as close as possible to the ANeffTM lateral contrast in TM mode so that the radius of curvature

  minimum admissible by the guide is the same in TE mode as in TM mode.

  3 As an example, we consider a guide characterized as follows: wavelength: 1550 nm, - refractive index of the substrate: 1.444, refractive index of the guiding layer: 1.45,

  - thickness of the guide layer: 5, lm.

  If you want the difference between the NeffTE lateral contrast in TE mode and the ANeffTM lateral contrast in TM mode to be less than 0.001, the contrasts

  optics that we can get quite falble wind.

  For a channel thickness of 0.05pm, the refraction index of the channel must be less than 1.70, which leads to an ANeffTE lateral contrast in TE mode of 0.003 and to an ANeffTM lateral contrast in TM mode of 0.002, the radius of

  o minimum curvature then being estimated between 20 and 25 mm.

  For a channel thickness of 0.10 m, the refraction index of the channel must be less than 1.60, which leads to an ANeffTE lateral contrast in TE mode of 0.004 and to an ANeffTM lateral contrast in TM mode of 0.003, the radius of

  minimum curvature then being estimated between 15 and 20 mm.

  For a channel thickness of 0.20 lm, the refraction index of the channel must be less than 1.55, which leads to an ANeffTE lateral contrast in TE mode of 0.006 and to an ANeffTM lateral contrast in TM mode of 0.005, the radius of

  minimum curvature then being estimated between 10 and 15 mm.

  The present invention thus relates to an optical waveguide having a reduced sensitivity to polarization and a contrast of high lateral index. According to the invention, a waveguide comprises a channel on an optical substrate, the refractive index of this channel being greater than that of the substrate, also comprises at least one guiding layer arranged on this channel, the index of s this guiding layer being greater than that of the substrate; moreover, the waveguide comprises an adaptation layer extending laterally on the side and

across the canal.

  The purpose of this adaptation layer is to reduce the sensitivity of the

polarization guide.

  o Preferably, the thickness of the adaptation layer is less than that of the channel. For example, it is between 20% and 60% of the thickness

of the canal.

  The adaptation layer decomposing into two bands each adjoining a lateral edge of the channel, the width of each of these bands is at

less equal to that of the canal.

  On the other hand, the refraction index of the adaptation layer is higher

to that of the canal.

  Advantageously, the waveguide comprises at least one covering layer disposed on the guiding layer, the index of this covering layer being lower than that of the guiding layer and that of the channel. According to a preferred embodiment, the channel is integrated into the substrate. Likewise, the adaptation layer is also integrated into the substrate. o Alternatively, the channel protrudes from the substrate and therefore the

  adaptation layer can also be arranged projecting on the substrate.

  It is preferable that the index of the guiding layer corresponds to that of the substrate

  multiplies by a factor greater than 1,001.

  According to an additional characteristic of the waveguide, the thickness of

  All of the guiding layers are between 1 and 20 microns.

  Preferably, the channel and possibly the adaptation layer

  result from ion implantation in the substrate.

  As an indication, the face of the substrate on which the implantation is carried out

ionic is made of silicon dioxide.

  2 o The invention also relates to a method of manufacturing a waveguide on an optical substrate comprising: - a step of defining a channel consisting in the production of a channel mask on the substrate, followed by - a step of ion implantation of the substrate comprising this channel mask, followed by - a step of removing the channel mask, a step of depositing at least one guiding layer on the substrate, the refraction index of this guide layer being higher than that of the substrate; this method further comprises, above the deposition step: a step of defining an adaptation layer consists of making an adaptation mask on the substrate, the adaptation layer extending laterally on either side of the canal, this step being followed by - a step for ion implantation of the substrate comprising the adaptation mask, followed by

  3 5 - a step of removing the adaptation mask.

  According to a first variant, this method of manufacturing a waveguide on an optical substrate comprises: - a first step of ion implantation of the substrate, - a step of depositing at least one guiding layer on the substrate, I the refractive index of this guide layer being greater than that of the substrate; and it further comprises, following this first step: - a step of defining an adaptation layer by application of an adaptation mask on the substrate and etching of this substrate, followed by - a second step of ion implantation of the substrate comprising this mask or adaptation to obtain a channel, followed by

  - a step of removing the adaptation mask.

  According to a second variant, the method comprises: - a first step of ion implantation of the substrate, - a step of defining a channel by application of an adaptation mask on the substrate and etching of this substrate, - a step depositing at least one guiding layer on the substrate, the refractive index of this guiding layer being greater than that of the substrate; and it further comprises, following the step of defining the channel: - a second step of ion implantation of the substrate comprising this mask or adaptation to obtain an adaptation layer, followed by

  - a step of removing the adaptation mask.

  Preferably, the method comprises a step of annealing the substrate which

  follows one of the stages of ion implantation.

  This method is also suitable for carrying out the different

  characteristics of the waveguide mentioned above.

  The present invention will now appear in more detail in the

  part of the following description of illustrative embodiments

  with reference to the appended figures which represent: - Figure 1, a diagram of a waveguide, - Figure 2, the manufacture of a waveguide according to a first method, - Figure 3, a first variant of this method, FIG. 4, a second variant of this method, and

  - Figure 5, a waveguide manufactured according to another method.

  With reference to FIG. 1, the substrate is made of silica or else it is made of silicon on which either a thermal oxide has been grown or a layer of silicon dioxide or another material has been deposited. It thus presents an upper face or optical substrate 11, commonly made of silicon dioxide, with a thickness of 5 to 20 microns, for example. The channel 12 produced by ion implantation, of titanium for example, is here integrated into the optical substrate. The adaptation layer here takes the form of two bands 13, 14 also produced by ion implantation and therefore they are integrated into the optical substrate. These two bands stetendent laterally from each of the blanks of channel 12. Wiles both have a thickness less than that of the channel, preferably between 20% and 60% thereof. Then the substrate 11 is covered with a guiding layer 15 of doped silicon dioxide which is produced for example by means of a chemical vapor deposition (PECVD for

  << Plasma Enhanced Chemical Vapor Deposition >>.

  The refractive index of channel 12 is naturally higher than that of silicon dioxide. The refraction index of the adaptation layer 13, 14 is itself higher than that of the channel 12. The guiding layer 15 of 5 microns s thickness, for example, has a refraction index greater than that of the optical substrate 11, for example 0.3%. Wile can possibly result from a stack of thin layers. Preferably, a covering layer 16 which may also consist of a stack of thin layers is provided on the guiding layer 15. This covering layer, also 5 microns o thick, has an index lower than that of the guiding layer 15 and a

  that of channel 12; in the present case it is made of non-doped silicon dioxide.

  With reference to FIG. 2a, a first method of manufacturing the waveguide comprises a first step which consists in producing a mask 22 on the optical substrate 21 to define the channel 23, this by means of a conventional photolithography process. . The mask 22 is made of resin, metal or any other material capable of constituting an insurmountable barrier for the ions during implantation. Optionally, the mask can be obtained by a

direct writing process.

  Channel 23 is produced by ion implantation of the mask substrate. For example, for a titanium implantation, the implantation dose is between 1016 / cm2 and 1048 / cm2 and the energy is between a few

  tens and a few hundred Key.

  Referring to Figure 2b, the mask is removed, for example by means

of a chemical etching process.

  With reference to FIG. 2c, the two bands 24, 25 of the wind adaptation layer obtained by masking and implantation, just like the channel 23. It should be noted that these two bands could have been produced before the channel. The substrate is then subjected to an annealing in order to reduce the losses to propagation within the channel 23. For example, the temperature is between 400 and 500 C, the atmosphere is controlled or else it is the 'outdoors,

  while the duration is of the order of a few tens of hours.

  o With reference to FIG. 2d, the guiding layer 26 is then deposited on the substrate 21 by means of any of the known techniques, provided that this leads to a material with low losses whose refractive index can be easily contrBle. Finally, the covering layer 27 is

  possibly deposited on the guide layer 26.

  With reference to FIG. 3a, a first variant of this manufacturing method comprises a first step which consists in implanting the whole of the

optical substrate 31.

  With reference to FIG. 3b, a second step consists in defining the two strips 34, 35 of the adaptation layer, this by masking and etching the

2 o substrate 31.

  With reference to FIG. 3c, the channel 33 is obtained by implantation through the mask used for the etching of the two strips 34, 35 of the layer

  adaptation. Then the mask is removed.

  The substrate is optionally subjected to annealing.

  With reference to figure 3d, finally wind successively deposited the

  guiding layer 36 and the covering layer 37.

  With reference to FIG. 4a, a second variant of the first manufacturing method comprises a first step which consists in implanting the

  all of the optical substrate 41, as in the first variant.

  Referring to Figure 4b, a second step is to define the

  channel 43, this by masking and etching of the substrate 41.

  With reference to FIG. 4c, the two bands 34, 35 of the wind adaptation layer obtained by implantation through the mask used for the etching of the channel 43. Then, the mask is removed, then the substrate is subjected to

annealing.

  With reference to FIG. 4d, finally wind successively deposited the

  guide layer 46 and cover layer 47.

  A second method harnesses ion exchange technology.

  In this case, the substrate is a glass containing mobile ions at relatively low temperature, a glass of silicates containing sodium oxide for example. This method is very similar to the first method except that the implantation steps are replaced by immersion steps in a bath containing polarizable ions such as silver or potassium. The pattern is thus produced by increasing the refractive index following the exchange o of the polarizable ions with the mobile ions of the substrate. Then, generally, the channel and the layer of adaptation wind buried by application of a field

  electric perpendicular to the face of the substrate.

  Referring to Figure 5, a third method implements the thin film technology. Generally, the upper face of the substrate 50 is made of silicon dioxide. A first layer with an index higher than that of silicon dioxide is deposited on the optical substrate by means of any known technique such as deposit by flame hydrolysis (<Flame Hydrolysis Deposition >> in chemical English terminology) in high or low pressure vapor phase and assisted or not by plasma,

  o evaporation under vice, cathodic pulverization or deposit by centrifugation.

  This layer is often doped silicon dioxide, silicon oxy-nitride, silicon nitride and it is also possible to use polymers or sole-gels. A mask defining the channel is then applied to the deposited layer. Then, this channel 51 is produced by a chemical etching or dry etching process such as plasma etching, reactive ion etching or etching

by ion beam.

  The mask is removed after engraving and a second layer is deposited. Another mask defining the two bands 53, 54 of the adaptation layer is then applied to the second layer before a new 3 o etching step. Then, wind deposited the guide layer 55 then

  possibly the covering layer 56.

  Of course, it is possible to realize first the two bands 53,

  54 of the adaptation layer and then the channel 51.

  This method requires an engraving operation which is difficult to control in terms of spatial resolution than in the surface state of the flanks of the channel 51 and of the bands 53, 54, characteristics which condition

  directly the propagation losses of the waveguide.

  The embodiments of the invention presented above have been chosen for their specific nature. However, it would not be possible to

  list in an exhaustive manner all the embodiments that cover

  this invention. In particular, any stage or any means described may be replaced by a stage or equivalent means without departing from the scope of the

present invention.

Claims (14)

  1) Waveguide comprising a channel 12, 23, 31 on an optical substrate 11, 21, 30, the refractive index of this channel being greater than that of the substrate, also comprising at least one guiding layer 15, 26, 35 arranged on said channel, the index of this guiding layer being greater than that of the substrate, characterized in that it comprises an adaptation layer 13-14, 24-25, 33-34   laterally extending on either side of said channel 12, 23, 31.   2) Waveguide according to claim 1, characterized in that the thickness of said adaptation layer 13-14, 24-25, 33-34 is less than the thickness o audit channel 12,23, 31.   3) Waveguide according to claim 2, characterized in that the thickness of said adaptation layer 13-14, 24-25, 33-34 is between 20% and   % of the thickness at said channel 12, 23, 31.   4) Waveguide according to any one of the preceding claims   characterized in that, said adaptation layer breaking down into two bands 13-14, 24-25, 33-34 each adjoining a lateral edge to said channel 12, 23,   31, the width of each of these bands is at least equal to that of the channel.   ) Waveguide according to any one of the preceding claims,   characterized in that the refractive index of said adaptation layer 13-14,   o 24-25, 33-34 is greater than that of channel 12, 23, 31.   6) Waveguide according to any one of the preceding claims,   characterized in that it comprises at least one covering layer 16, 27, 36 arranged on said guiding layer 15, 26, 35, the index of this layer of   overlap being lower than that of the guiding layer and that of the channel.   s 7) waveguide according to any one of the preceding claims,   characterized in that said channel 12, 23 is integrated into said substrate 11, 21.   8) Waveguide according to any one of the preceding claims,   characterized in that said adaptation layer 13-14, 24-25 is integrated into said substrate 11.   o 9) waveguide according to any one of claims 1 to 6,   characterized in that said channel 3 1 protrudes from led it on base 30.   ) Waveguide according to any one of claims 1 to 6 or 9,   characterized in that said adaptation layer 33-34 protrudes from said substrate 30.   11) Waveguide according to any one of the preceding claims,   characterized in that the refractive index of said guiding layer 15, 26, 35   is that of the substrate 11, 21, 30 multiplied by a factor greater than 1, 001.   12) Waveguide according to any one of the preceding claims,   characterized in that the thickness of the set of guide layers 15, 26, is between 1 and 20 microns.   13) Waveguide according to any one of the preceding claims,   characterized in that said channel 12, 23 results from an ion implantation in said substrate 11, 21.   o 14) waveguide according to any one of the preceding claims,   characterized in that said adaptation layer 33-34 results from implantation ionic in said substrate 11, 21.   ) Waveguide according to any one of the preceding claims,   characterized in that the face of the substrate 11, 21, 30 on which the ion implantation is carried out is made of silicon dioxide. 16) Method of manufacturing a waveguide on an optical substrate comprising: - a step of defining a channel consists in the production of a channel mask 22 on said substrate 21, followed by - a step of ion implantation of the substrate comprising said channel mask 22, followed by - a step of removal from said channel mask 22, - a step of depositing at least one guiding layer 26 on the substrate, the refraction index of this guide layer being higher than that of the substrate; characterized in that it further comprises, preceding said deposition step: - a step of defining an adaptation layer consists of the production of an adaptation mask on said substrate 21, said adaptation layer s extending laterally on either side of said channel 22, step followed by 30 - a step of ion implantation of the substrate comprising said adaptation mask, followed by   - a step of removing said adaptation mask.   17) Method for manufacturing a waveguide on an optical substrate comprising: s - a first step of ion implantation of the substrate 31, - a step of depositing at least one guiding layer 36 on the substrate, I ' refractive index of this guide layer being greater than that of the substrate; characterized in that it further comprises, following said first step: - a step of defining an adaptation layer 34, 35 by application of an adaptation mask on the substrate 31 and etching of this substrate, followed by - a second step of ion implantation of the substrate comprising said adaptation mask to obtain a channel 33, followed by   - a step of removing said adaptation mask.   o 18) Method of manufacturing a waveguide on an optical substrate comprising: - a first step of ion implantation of the substrate 41, a step of defining a channel 43 by applying an adaptation mask on the substrate 41 and etching of this substrate, - a step of depositing at least one guide layer 46 on the substrate, the refractive index of this guide layer being greater than that of the substrate; characterized in that it further comprises, following said step of defining the channel: o - a second step of ion implantation of the substrate comprising said adaptation mask to obtain an adaptation layer 44, 45, followed by   - a step of removing said adaptation mask.   19) Method according to any one of claims 16 to 18,   characterized in that it comprises a step of annealing the substrate 21, 31, 41,   which follows one of the stages of ion implantation.   ) Method according to any one of claims 16 or 19,   characterized in that it comprises a step of depositing a covering layer 27, 37, 47, 56 on said guiding layer 26, 36, 46, 55, the index of this covering layer being lower than that of the guiding layer and has that of channel 23, 31, 41, 50.   21) Method according to any one of claims 16 to 20,   characterized in that the index of said guiding layer 26, 36, 46, 55 is   that of the substrate 21, 31, 41, 50 multiplies by a factor greater than 1, 001.   22) Method according to any one of claims 16 to 21,   characterized in that the thickness of the set of guide layers 26, 36,   46, 55 is between 1 and 20 microns.   23) Method according to any one of claims 16 to 22,   characterized in that the face 21, 31, 41, 50 of the substrate on which is produced