Optical waveguides – With optical coupler
Reexamination Certificate
1999-09-17
2002-04-23
Schwartz, Jordan M. (Department: 2873)
Optical waveguides
With optical coupler
Reexamination Certificate
active
06377722
ABSTRACT:
BACKGROUND OF THE DRAWINGS
The invention pertains to a polymeric phased array comprising an input coupler with N inputs and an output coupler with M outputs, N and M being natural numbers greater than or equal to 1 wherein the couplers are optically connected by means of an optical array comprising a series of optical waveguides, each of which differs from a neighbour in optical path length by a predetermined fixed amount.
Phased arrays, also denoted as, e.g, “Phasars,” “Array waveguide multiplexers,” or “Arrayed Waveguide Gratings,” manufactured of a polymeric material are known from, for instance, M. B. J. Diemeer et al., “Polymeric phased array wavelength multiplexer operating around 1550 nm,”
Electronic Letters, Jun.
6th, 1996, Vol. 32, No. 12.
This publication concerns phasars comprising curved waveguides of mutually differing physical lengths and mentions that polymeric phased arrays (i.e., phased arrays comprising a polymer core and at least one polymer (top) cladding) advantageously offer optical fiber compatibility combined with low cost and the possibility of using large substrates for the fabrication. Owing to the use of large substrates, the polymeric phased arrays can be integrated with other (polymeric) optical components, such as switches, which allows the manufacture of add/drop multiplexers capable of individual routing of the different wavelength channels.
However, an interferometric device like the polymeric phasar is very sensitive to changes in temperature and physical ageing of the polymer of which it is manufactured.
The invention has for its object to reduce or even obviate the said sensitivity. This is achieved by a polymeric phased array as described in the first paragraph wherein the physical length of all the waveguides (in the array) is substantially equal.
SUMMARY OF THE INVENTION
In accordance with an aspect of the invention, there is provided, a polymeric phased array comprising an MMI input coupler with N inputs and an MMI output coupler with M outputs, N and M being natural numbers greater than or equal to 1, wherein the couplers are optically connected by means of an optical array comprising a series of optical waveguides, each of which differs from a neighbour in optical path length, characterized in that the physical length of all the waveguides in the array is substantially equal.
Although a free space coupler is suitable, MMI couplers provide significant and advantages.
It was found that, as a result of the substantially equal lengths of the waveguides, the phenomena discussed above influence the optical path lengths of all the waveguides to (substantially) the same extent. Consequently, the differences in optical path lengths of the waveguides, on which differences the operational principle of a phased array is based, remain virtually constant, and the functioning of the phased array is effectively unaffected.
It is preferred that the maximum deviation from the average (arithmetical mean) of the physical length of the waveguides is smaller than 5 percent, preferably smaller than 1 percent or even smaller than 0.5 percent, of the said average, because with such a small deviation the central wavelength is sufficiently fixed for practical use.
In a preferred embodiment of the polymeric phased array according to the present invention the waveguides run straight. Additional advantages of a phasar comprising straight and parallel waveguides are that such a phasar is compact, has a relatively low insertion loss due to the absence of bends in the waveguides, allows economic; use of wafers, and allows a larger integration density. Also, the production of phasars is simplified because the phasars, which are densely packed on a single wafer, can be separated by means of a single and straight cut (as opposed to a complicated cut which manoeuvres between curved phasars).
The straight phasar according to the present invention is even more compact when the input coupler and
1
the output coupler are combined and the waveguides are provided with a mirror or a facet or endface that functions as a mirror. This kind of waveguide can be manufactured, for instance, by simply dividing a straight phasar up into two equal parts (by means of a cut perpendicular to the waveguides of the array) and depositing a reflective coating or mounting a mirror on the obtained endfaces.
Phasars comprising combined couplers and a mirror surface are known in themselves, e.g., from H. Okayama et al., “Reflective Waveguide Array
Demultiplexer in LiNnO
3,”
Journal of Lightwave Technology
, Jun. 1996, Vol. 14, No. 6, pp. 985-990. From this publication it can be seen that prior art “half phasars require, besides the usual curved section, additional straight sections normal to the mirror surface in order to allow a mode confined in the waveguides to settle and avoid losses during reflection. ” Consequently, the half phasar of the prior art requires its own “custom made” manufacturing process, whereas the half phasars of the invention can, as mentioned above, be manufactured by dividing up an existing specimen.
It is preferred that the polymeric phased array is a so-called planar structure. Free-space couplers are considered the most suitable couplers because of their wavelength independence. It has been found that Multi Mode Interferometers, also, denoted, as MMI couplers are the most suitable for this application.
One possible way of varying the optical path length of the waveguides whilst keeping their physical length constant consists in using different polymers having a refractive index which differs (by a predetermined fixed amount) for each of the waveguides in the array. Since this requires a large number of different (blends of) polymers and process steps, it is preferred that the waveguides comprise serial zones of different refractive indices. Thus, the optical path length of each of the waveguides is determined by the refractive indices and the lengths of the serial zones.
If a certain phasar comprises, for example, fifty waveguides of equal physical length but with the optical path length of each waveguide differing from that of its nearest neighbour(s) by a predetermined fixed amount, the waveguides may consist of, successively, a zone having a refractive index n
1
, a zone having a refractive index n
2
, and a zone having, again, a refractive index n
1
, with n
2
>n
1
. By increasing the length of the zone having a refractive index n
2
, the optical path length is increased. Thus, the optical path length of each of the waveguides can be adjusted by varying the lengths of the different zones so as to form the required grating.
Waveguides comprising serial zones and one particular way of manufacturing them are described In more detail in T. Watanabe et al., “Novel ‘serially grafted’ connection between functional and passive polymer waveguides,”
Appl. Phys. Lett
. 65 (10), Sep. 5, 1995. Other ways of making waveguides with the said serial zones of course are not excluded.
In another embodiment according to the present invention at least one of the waveguides comprises a polymer which allows actively induced variation of the refractive index, for instance using the thermo-optical or electro-optical principle which is well-known to the skilled person.
By using such a polymer (either over the entire length of the waveguide or in one or more zones) the central wavelength and/or the wavelength peaks in the image plane in the output free-space coupler can be adjusted during operation by powering a heating element positioned near the waveguide. In the latter instance, it is preferred that at least some of the heating elements can be individually controlled.
It is noted that EP 717 295 discloses an MxO multiplex/demultiplex device comprising optical fibers or silica waveguides which function as a grating. Although waveguides of equal length are mentioned, it is apparent from the example illustrated by
FIG. 3
that equal is not to be taken literally, because evanescent coupling regions require the optical fibers to be in close contact, whereas in the grating area the o
Greene Kevin E.
JDS Uniphase Inc.
Lacasse Randy W.
Lacasse & Associates
Schwartz Jordan M.
LandOfFree
Polymeric phased array does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polymeric phased array, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymeric phased array will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2847214