Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2001-07-02
2003-12-16
Prasad, Chandrika (Department: 2839)
Optical waveguides
With optical coupler
Plural
C385S037000
Reexamination Certificate
active
06665466
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrayed waveguide grating (AWG: Arrayed Waveguide Grating) type optical multiplexer/demultiplexer applicable as a wavelength selection element to wavelength division multiplexing (WDM: Wavelength Division Multiplexing) transmission systems.
2. Related Background Art
The AWG type optical multiplexer/demultiplexers (hereinafter referred to as AWG circuits) are widely applied to the wavelength selection elements in the WDM transmission systems, as wavelength filters enabling extraction or insertion of a specific wavelength by interference. The AWG circuits do not require so precise machining as required by diffraction gratings or so precise multilayer film formation as required by interference films, but they can be constructed by ordinary microprocessing such as lithography, etching, and soon. Therefore, the AWG circuits are expected to develop into dominant optical components in the future WDM transmission systems, also including the possibility of integration with other light waveguide elements.
Such AWG circuits have the structure in which an input waveguide, an input slab waveguide, channel waveguides (phased array) of mutually different lengths, an output slab waveguide, and output waveguides are integrated on a single substrate.
SUMMARY OF THE INVENTION
FIG. 6
is a plan view to show the waveguide structure of light output part in a conventional AWG circuit (optical multiplexer/demultiplexer). In this AWG circuit, ends of channel waveguides
10
of mutually different lengths are connected at intervals d to one connection surface of output slab waveguide
20
. Ends of output waveguides
30
provided corresponding to beams of respective channel wavelengths, i.e., corresponding to respective signal channels are connected to the other connection surface of the output slab waveguide
20
.
In general, the connection surface of the output slab waveguide
20
to which the ends of channel waveguides are connected, is designed to work as a convex lens, and one end of each channel waveguide is placed on the circumference of a circle of the radius s (slab length) with the center at a position O
1
where the light of the center channel wavelength converges. On the other hand, one end of each output waveguide connected to the other connection surface of the output slab waveguide is placed on the circumference of a Rowland circle
200
having the diameter equal to the slab length (reference is made to Japanese Patent No. 2599786 and “Applied Optics I,” the first edition published Jul. 20, 1990 by Baihukan).
However, the signal of the center channel wavelength was surely converged at the point O
1
, whereas there was the possibility that there occurred decrease of light collection efficiency and distortion of wavelength characteristics due to aberration or the like with the signals of the other channel wavelengths to be converged at points except for the point O
1
on the Rowland circle. Specifically, there occurs loss variation of about 4 dB among the channel wavelengths, as illustrated in
FIG. 7
, in loss spectra of the respective output waveguides (hereinafter referred to as output CHs) in the conventional AWG circuit.
FIG. 8
schematically shows the loss spectrum (of the spectral width W
1
) in the output waveguide (output CH located near the center) corresponding to the center channel wavelength and the loss spectra (of the spectral width W
2
(>W
1
)) in the output waveguides (output CHs located near the periphery) corresponding to the longest channel wavelength and to the shortest channel wavelength in the signal wavelength band out of the loss spectra illustrated in FIG.
7
. As also seen from this
FIG. 8
, the loss in each output CH increases with increase in the distance from the output CH located near the center, while with increase in the distance from the output CH located near the center, the shape of the loss peak becomes duller and the spectral width of the loss spectrum in each output CH also increases from W
1
to W
2
(>W
1
) (distortion of wavelength characteristics); therefore, there was the problem that the wavelength separation accuracy considerably degraded when the signal wavelength band was totally shifted to the longer wavelength side or to the shorter wavelength side.
The present invention has been accomplished in order to solve the problem described above and an object of the invention is to provide an optical multiplexer/demultiplexer having structure for positively compensating for the distortion due to the aberration of wavelength characteristics or the like among the signal channels and permitting effective reduction of the loss variation or the like.
An optical multiplexer/demultiplexer according to the present invention is an AWG type optical multiplexer/demultiplexer applicable as a wavelength selection element to the WDM transmission systems, which comprises a substrate, at least one input waveguide provided on the substrate, a first slab waveguide, a plurality of channel waveguides, a second slab waveguide, and a plurality of output waveguides provided corresponding to respective signal channels.
In the optical multiplexer/demultiplexer according to the present invention, each of the above first and second slab waveguides has a predetermined slab length. The slab length is normally equal to a focal length of an optical input end functioning as a lens surface of each slab waveguide. The above input waveguide is a waveguide for guiding each of the signals of channel wavelengths set as signal channels at predetermined wavelength intervals, to the first slab waveguide, and an optical output end thereof is connected to the optical input end face of the first slab waveguide. The above channel waveguides are waveguides of mutually different lengths, which are flatly arrayed on the substrate in a state in which optical input ends thereof are connected to an optical output end face of the first slab waveguide so as to place the first slab waveguide between the channel waveguides and the input waveguide while optical output ends thereof are connected to the optical input end face of the second slab waveguide so as to place the second slab waveguide between the channel waveguides and the output waveguides. Further, the above output waveguides are waveguides flatly arrayed on the substrate in a state in which optical input ends thereof are connected to an optical output end face of the second slab waveguide, which are waveguides for individually taking out the signals of the channel wavelengths set at the predetermined wavelength intervals.
Particularly, the optical multiplexer/demultiplexer according to the present invention is characterized in that an optical input end of at least either one of the output waveguides is located at a position apart from the optical input end face of the second slab waveguide by a distance shorter than a focal length of the optical input end face of the second slab waveguide. It is preferable that the optical input ends of two output waveguides located outermost out of the output waveguides be placed on the circumference of a Rowland circle having a diameter equal to the focal length of the optical input end face of the second slab waveguide and that the optical input ends of the rest output waveguides excluding the two output waveguides out of the output waveguides be placed inside the Rowland circle and on a line connecting the optical input ends of the two output waveguides. In other words, it is preferable that the optical input ends of at least two output waveguides out of the output waveguides be located at positions where the optical output end face of the second slab waveguide intersects with the circumference of a Rowland circle having a diameter equal to the focal length of the optical input end face of the second slab waveguide. Here the line connecting the optical input ends of the two output waveguides located outermost out of the output waveguides may be part of a straight line (which corresponds to a chord of the above
McDermott & Will & Emery
Prasad Chandrika
Sumitomo Electric Industries Ltd.
LandOfFree
Optical multiplexer/demultiplexer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical multiplexer/demultiplexer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical multiplexer/demultiplexer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3145506