Optical waveguides – With optical coupler – Particular coupling function
Reexamination Certificate
1999-06-04
2001-07-31
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling function
C385S027000, C385S015000, C385S011000, C385S037000, C385S122000
Reexamination Certificate
active
06269205
ABSTRACT:
TECHNICAL FIELD
The present specification relates to mode coupling in waveguides, and more particularly, to optical devices based on energy transfer between different waveguide modes.
BACKGROUND
An optical waveguide, such as an optical fiber or a dielectric slab waveguide formed on a substrate, can interact and confine optical energy in one or more waveguide modes depending on the design of the waveguide. A waveguide mode can be characterized by a number of mode parameters such as the spatial distribution of optical energy, the propagation constant, and the polarization state. Two different modes, either coexisting in the same waveguide or respectively residing in two separate waveguides, may couple with each other to exchange their energy under proper conditions. Such mode coupling can be used to perform various optical operations on guided optical waves. For example, devices like optical couplers and switches can be made by using waveguides.
Energy transfer from one optical wave to another co-propagating wave is desirable in many applications such as optical communication systems. Mode coupling between two co-propagating modes in a multimode waveguide may be used to achieve such operation. A periodic index perturbation that forms a grating along the waveguide can be used to couple the modes when the propagation constants of the two modes satisfy a Bragg-type condition. See, e.g., Yariv,
Optical Electronics
, Chapter 13, Saunders Publishing (1991).
For two co-propagating modes A and B to couple in a grating of a period A in the waveguide, the Bragg condition is:
β
A
-
β
B
=
±
m
2
π
Λ
,
for
m
=
1
,
2
,
3
,
…
(
1
)
where &bgr;
A
, &bgr;
B
are the propagation constants for modes A and B, respectively. The power conversion may be expressed by
P
B
(
Z
)=
P
B
(0)cos
2
(
K
z
), (2)
and
P
A
(
z
)=
P
B
(0)sin(
K
z
), (3)
where P
B
(0) is the power of the mode A before entering the grating and
K
is the coupling coefficient
K
between modes A and B in the grating. Hence, power exchange between modes A and B varies sinusoidally with
K
z. If the interaction length z is controlled at L=Π/(2
K
) or its multiples, then the power of the mode B can be completely transferred into the mode A.
However, a precise control of the grating length for such phase matching is difficult in practical devices. This may be in part due to the unavoidable variations in manufacturing the grating in the waveguide and in part due to variations in the coupling parameter (
K
L) caused by environmental fluctuations during operation. In addition, since the desired coupling length L=Π/(2
K
) usually has a strong dependence on both the wavelength and the polarization, the above coupling device may only operate in a narrow band and can be subject to degradation in performance caused by fluctuations in polarization. Furthermore, because the difference between the propagation constants of modes A and B is usually small, the required grating period &Lgr;=2Πm/|&bgr;
A
−&bgr;
B
| is large. Hence, it is difficult to make this type of grating couplers compact.
SUMMARY
In recognition of the above, the present disclosure includes optical waveguide devices based on energy transfer between two copropagating modes via a third mediating mode by using one or more waveguides. The use of the third mediating mode can make the devices relatively insensitive to design parameters such as the coupling length and hence increase flexibility in device design. Other benefits include low insertion loss, reduced sensitivity to polarization, and operation at a narrow band an a broad band.
One embodiment of this type of waveguide devices includes a first optical terminal to receive optical energy in a first waveguide mode, a first wave-coupling region structured to couple at least a portion of the first waveguide mode into a second waveguide mode, a second wave-coupling region structured to couple the second waveguide mode into a third waveguide mode, and a second optical terminal coupled to the second wave-coupling region to output optical energy in the third waveguide mode. The second waveguide mode is different from the first and second waveguide modes. The first and third waveguide modes are copropagating with each other.
The two wave-coupling regions may be two different gratings formed in a single waveguide that is structured to support at least the first, second, and third waveguide modes. The waveguide includes a first grating and a second grating that work in combination to transfer energy between the copropagating first and third modes. The first grating is operable to couple one mode of the first and second modes into the other mode propagating in the opposite direction while being transmissive to the third mode and other modes. The second grating is operable to couple one mode of the second and third modes into the other mode propagating in the opposite direction while being transmissive to the first mode and other modes. The second grating is positioned relative to the first grating so that an optical wave in the second mode, if generated from one of the first and second gratings by converting a transmitted wave from the other grating, propagates towards at least a portion of the other grating to effect energy transfer between copropagating optical waves respectively in the first and third modes.
Three different waveguides may also be coupled to effect the first and the second coupling regions. One implementation uses a first waveguide structured to support the first waveguide mode and having an input as said first optical terminal, a second waveguide structured to support the second waveguide mode that copropagates with the first waveguide mode, and a third waveguide structured to support the third waveguide mode and having an output as the second optical terminal. The first waveguide has a segment close to a first portion of the second waveguide to allow evanescent coupling therebetween to form the first wave-coupling region. The third waveguide has a segment close to a second portion of the second waveguide to allow evanescent coupling therebetween to form the second wave-coupling region. The first and second portions in the second waveguide partially overlap each other and the first portion is closer to the second optical terminal than the second portion.
The first and third waveguides may be structured so that the first and third modes are phase matched to effect an efficient coupling in a wide range of wavelengths. A waveguide control may be implemented to control at least one of the first and the third waveguides to switch the device between a coupling state and a non-coupling state.
These and other aspects and associated advantages will become more apparent in light of the detailed description, the accompanying drawings, and the appended claims.
REFERENCES:
patent: 5093876 (1992-03-01), Henry et al.
patent: 5278926 (1994-01-01), Doussiere
patent: 5448664 (1995-09-01), Zuev
patent: 5517589 (1996-05-01), Takeuchi
patent: 5524156 (1996-06-01), Van Der Tol
patent: 5903683 (1999-05-01), Lowry
patent: 5940556 (1999-08-01), Moslehi et al.
patent: 5995691 (1999-11-01), Arai et al.
patent: 6049643 (2000-04-01), Lee et al.
Peral Eva
Yariv Amnon
California Institute of Technology
Fish & Richardson P.C.
Healy Brian
LandOfFree
Optical devices based on energy transfer between different... 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 devices based on energy transfer between different..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical devices based on energy transfer between different... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2458056