JP2002514783A - Multimode coupler based on miniaturized interference - Google Patents

Abstract

(57) Abstract: MMI coupler according to the invention has a smooth continuous inwardly tapering sidewalls which define the width of the multimode region (W ₁₎ along the propagation axis of the device (301) . The inward taper reduces the average width of the device as compared to known couplers having straight sidewalls (202), eliminating lithographic gap filling as well as unwanted optical coupling between access waveguides. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The United States Government has rights in the invention, and a contract F49620-95-040, negotiated by the Defense Research Program / Air Force Ministry of Science.
And has a limited right to require the proprietor of the patent to enter into a licensing agreement with another person on reasonable terms provided by Condition 3.

[0002] Multimode (MMI) devices based on the background interference invention is an important element of the optical circuits integrated. The operation of the optical MMI device is based on the principle of self-imaging of a multimode waveguide, where the input field profile is reproduced as a plurality of "images" at periodic intervals along the waveguide propagation axis. This MMI
The device can function, for example, as a power splitter multimode other device. The basic known structure of an MMI coupler requires a relatively wide multimode waveguide region designed to support a large number of mode lights. A number of relatively narrow access waveguides are located at the entrance end of the MMI region to allow light to enter and exit the relatively wide multimode waveguide region. A device configured in this manner is generally called an N × M coupler, where N and M are the number of input-side waveguides and the number of output-side waveguides, respectively (both are known as access waveguides). Is). Review MMI devices from Soldano and Pennings
, “Optical Multi-Mode Interference Devices Based on Self-Imaging”, Jo
urnal of Lightwave Technology, Vol. 13, No. 4, April 1995.

[0003] Integrated optical circuits that currently require an NxM power splitter include ring lasers, Maffer-Zehnder interferometers, and optical switches. PABasse, M. Bachmma
n, LBSoldano, and MKSmit, Optical Bandwidth and Fabrication Tolera
nces of Multimode Interference Couplers ”, Journal of Lightwave Technol
ogy, Vol. 12, pp. 1004-1009, 1994, by LBSoldano and ECMPennings, Opt.
ical Multi-Mode Interference Devices Based on Self-Imaging Principles an
d Applications ”, Journal of Lightwave Technology, Vol. 13, pp615-627, 19
95, and LHSpiekman, YSOei, EGmetaal, FHGroen, I. Moerman, and M
.K.Smit, Extremely Small Multimode Interference Couplers and Ultrasho
rt Bends on InP By Deep Etching ", IEEE Photon. Technol. Lett., Vol 6, pp.
1008-1010, 1994. The most important current MMI structure is a 2x2 coupler from all these device applications, the most common being the "3-dB" power that separates the input signal into two halves of the output signal Splitter. Other MMI-based devices are mode-width expander multi-mode spot size converters, which have been used to increase or eliminate the intensity distribution of periodic images within the multi-mode region. For example, Simpson et al., “Mode-Width Expanders Based on the Self Effect in Tapered Multimode G
aAs / AlGaAs Waveguides ", Proc. 7th Conf. on Int. Opt., 1995 at 29. For example, improvements in telecommunications networks that require flexibility, increased capacity, and reconfigurability are expected to increase applications, all of which use optical integrated circuits for optical communications. Can be enhanced. To date, known MMI-based devices that maintain a substantially uniform power distribution throughout the output image are configured with straight sidewalls that define the MMI area.

In order to mass-produce integrated circuits for these MMI devices and make better use of them, it is desirable to reduce the dimensions of these devices and improve manufacturing tolerances. At present, for example, linear "3-dB" MMI couplers have been reduced to extremely small dimensions, with typical limits of several hundred microns. Reducing the length of the MMI device is easily achieved by controlling the width W _{MMI of the} MMI area. The linear 3-dB coupler has a device length L _MMI that is proportional to the square of the width of the MMI device, ie, L _MMI ∝W _MMI ² .

For a straight 2 × 2 coupler, the width W _MMI must be less than or approximately equal to the combined width of the MMI region between the two input and access waveguides. This total width is a practical constraint in further reducing device size / length. At least the following restrictions exist.

First, the width of the area between the set of access waveguides that defines the lower limit of the width W _MMI cannot be less than the allowable manufacturing tolerance. When devices are patterned on a semiconductor wafer, manufacturing defects such as lithographic gap filling can occur. These defects can be caused by optical (or electronic) proximity effects that occur during photolithography (or electron beam lithography) patterning, low image contrast of the optics (ie, low focusing or image contrast in air), or Can be caused by inadequate chemical treatment. These defects will limit the width of the area between the access waveguides in practical application. For example, "Micr
olithgraphy process Technology for IC Fabrication ", D. Elliott, New Yor
k: Magraw-Hill Book Co., 1986, and "VLSIFabrication Principles", 2nd ed
., S. Ghandi, New York, John Wiley and Sons, Inc., 1994.

Second, if the access waveguides are too close, undesirable pattern transmission between the waveguides will occur. This parasitic optical phenomenon results from an effect known as optical coupling and acts to limit the spacing between the waveguides, ie the width W _MMI in practical application. Optical or directional couplings are available from A. Yariv, Opti
Cal Electronics, 4th ed., New York: Holt, Reinhard, and Winston, 1991.

Third, it is possible to reduce the width W _MMI by reducing the width of the access waveguide while keeping the distance between the waveguides constant, but this causes unacceptable signal loss. There is a risk. For example, the loss due to etching that introduces the roughness of the waveguide wall results in a larger loss in a narrower waveguide, unlike a wider waveguide. Thus, if the thickness waveguide is too thin, unacceptable transmission losses may occur. In this regard, R. Deri and L. Schiavone,
Scattering in Low-Loss GaAs / AlGaAs Rib Waveguide ”, Appl. Phys. Lett., Vol.
.51, pp. 789-91, 1987 and M. Steyn, P. Kendall, R. hewson-Browne, P. Robson, `` Scattering Loss From Rough Sidewalls in Semiconductor Rib Waveguide ''
, Electronics Letters, Vol. 25, pp. 1231-2, 1989.

Fourth, because the manufacturing width tolerance ΔW of the MMI region is proportional to the square of the width W _WG of the thickness waveguide, if the access waveguide is too thin, the required manufacturing “width” "Tolerances" can cause practical problems or become impossible to achieve with current manufacturing processes. The "width tolerance" [Delta] W is the change in foreground width of the MMI region caused by acceptable manufacturing errors while maintaining the imaging capability of the MMI device. Since the ΔWαW _WG ^2, it is desirable to ensure a greater manufacturing tolerances to further increase the width of the access waveguides. Optical Ba by P. Besse, M. Bachmann, L. Soldano, and M. Smit
ndwidth and Fabrication Tolerances of Multimode Interference Couplers ''
, Journal of Lightwave Technology, Vol. 12, pp. 1004-9, 1994.
On the other hand, in a normal linear MMI coupler, if the width of the access waveguide is further increased, the overall device width increases, and L _MMI ∝W _MMI ² , thereby increasing the size / length of the device.

Accordingly, it is an object of the present invention to (1) reduce the average width W _MMI to enable the manufacture of smaller MMI devices, and (2) to sufficiently separate the access waveguides of the MMI device. Lithography gap filling or optical coupling can be avoided while keeping the average width W _{MMI and} thus the overall size / length of the coupler small, and (3) the average width W _MMI and the corresponding length L _Wider access waveguides can be used without increasing the _MMI , thereby reducing transmission loss and increasing the width tolerance .DELTA.W to pattern split the output image of an MMI device having straight sidewalls. It is an object of the present invention to provide an N × M MMI coupler which has substantially the same functions and eliminates the problems of the prior art.

Other uses and advantages of the present invention will be described in detail with reference to the disclosed drawings.

SUMMARY OF THE INVENTION The present invention maintains a uniform power split ratio for an MMI device having straight sidewalls, while providing a smooth, continuous, inwardly curved tapered sidewall defining the MMI region. The above-mentioned disadvantages are eliminated by providing an MMI coupler having an even smaller average width of the MMI device than a corresponding device having straight side walls. The inwardly curved taper reduces the average width of the coupler and can achieve various beneficial properties.

First, the overall length of the MMI coupler is proportional to the square of the average width of the MMI region, and L _MMI
The ∝W _MMI ² results in a relatively gentle taper that reduces the average width, resulting in a much smaller coupler than previously available. Further, since a shorter device can be realized without reducing the width at the end point of the coupler, the optical coupling can be avoided by sufficiently separating the waveguides.

Second, if realization of the shortest device is not the purpose of the design, the use of the tapered sidewalls according to the present invention allows the coupler at the end point of the coupler without increasing the device length. Can be increased. This allows the access waveguides to be farther apart, eliminating manufacturing defects such as the lithographic gap filling described above. Alternatively, by using a narrower access waveguide, transmission loss can be minimized and the above-mentioned manufacturing tolerance ΔW of the width of the MMI region can be further increased.

By using the device according to the present invention, the size can be minimized, the optical coupling can be reduced, the transmission loss can be reduced, the lithographic gap can be closed, and the manufacturing tolerance can be further increased. it can. In certain applications,
Which benefits are maximized is a design choice.

[0016] be described with reference to preferred embodiments in the accompanying figure 1-8 by the detailed description the invention.

As mentioned above, various MMI-based devices are useful elements in integrated optical circuits. The preferred embodiment of the present invention will be described with reference to one more general application, namely a power splitter. On the other hand, it will be apparent to those skilled in the art that the present invention can be applied to other MMI-based devices such as, for example, expanders or spot size converters. These devices maintained approximately equal power splits at the output stage and were designed to use straight sidewalls.

FIG. 1 shows a known structure of a power splitter based on a straight 3-dB MMI.
The device comprises a relatively narrow input access waveguide (101) and an input optical signal (1).
05), a relatively wide multi-mode waveguide region (103) capable of transmitting a large number of mode lights when it enters, and two relatively narrow widths for outputting two images of an input optical signal. An output access waveguide (107). Based on the principle of periodicity self-imaging, where the input signal is periodically reconstructed as a single image or as multiple images along the propagation axis Z of the multimode waveguide region, the original input signal (1
The dimensions of the multimode region (103) are defined so that the two images of (05) are output via the output access waveguide (107). Each output signal (109) has approximately half the energy of the input signal. Such a device is commonly referred to as a 3-dB MMI power splitter.

As shown in FIG. 1, the device is dimensioned such that when the multi-mode region starts at Z = 0, the output image appears along the propagation axis Z at Z = L _MMI. I have. The width of the multi-mode region (103) is denoted by W ₀ and needs to be wide enough so that a large number of guided mode lights are effective on the principle of interference. In the case of the linear MMI device shown in FIG. 1, the width W _{MMI of the} MMI region is constant along the propagation axis. A linear 3-dB coupler designed using general imaging has a device length represented by the following formula: L _MMI = 2n _eff W _MMI ² / λ where n _eff is an effective refractive index, λ is the wavelength. When the high-contrast waveguide is strongly restricted, the MMI region width W _MMI appearing in the above equation is the physical width of the MMI region. On the other hand, it is necessary to consider the Goos-Haenchen effect as if you only weaken the low contrast structure W _MMI becomes effective width. Sold mentioned above
See nano, et al. For the purposes here, W _MMI is considered to be the physical width of the MMI area.

Therefore, since L _MMI ∝W _MMI ² , the most effective means of controlling the overall length of the device is to scale W _MMI . On the other hand, as discussed in the background section, there are practical limitations imposed by lithographic gap fill-in, optical coupling, transmission losses or infeasible or unattainable manufacturing width tolerances. To date, couplers based on the smallest known straight line 3-dB MMI have been achieved with a length reduced to 107 μm. See Spiekman et al. Cited above. The typical length of the smallest available 3-dB coupler is a few hundred micrometers. According to the invention, the actual length can be reduced to 50 μm or less.

A 3-dB MMI based coupler according to the present invention is shown in FIG. The main difference between the device shown in FIG. 1 and the device shown in FIG. 3 is that each opposing side wall (301) of the MMI region of FIG. 3 is inwardly directed toward the opposing side wall instead of being straightened. It is curved. The opposing side walls (301) define the width W _MMI of the MMI region at each position along the propagation axis Z, so that by bending inward, the average width of the MMI region is reduced by the corresponding linear MMI device shown in FIG. It becomes smaller than the average width. By reducing the average width, in light of the relationship L _MMI ∝W _MMI ² described above,
The length L _MMI becomes shorter.

In FIG. 3, the 3-dB MMI device according to the present invention includes an input optical signal (305
) Can be propagated through two relatively narrow input access waveguides (303).
) And a relatively wide multi-mode region that can maintain a sufficiently large number of mode lights and enables imaging performance based on interference of the MMI region when an input optical signal is incident (
307) and two relatively narrow output access waveguides (309) for outputting an image of the input signal. The output image (311) is generally called a bar state (bar stste) and a cross state (cross stst). 3-dB
The overall dimensions of the coupler are set such that the two output signals appear at the position Z = _LMMI . On the other hand, the width W _MMI Mean is smaller than the width of the corresponding linear 3-dBMMI device, the total length L _MMI consists more shortened based on the relationship of L _MMI αW _MMI ^2.

In order to function in accordance with the present invention, the tapered portion must be smoothly continuous according to a continuous derivative along the propagation axis and bend inwardly toward opposing sidewalls to reduce the average width of the MMI region. There is. If the derivative of the tapered portion is discontinuous, such as the linear tapered portion (202) of the triangular meter of FIG. 2, undesired power transfer will occur between output images, as described below. It is also advantageous according to the invention to define the maximum curvature of the tapered portion as characterized by the second derivative along the propagation axis of the width W _MMI such that the guided mode light is substantially maintained. Mode conversion in the MMI region that leads to degradation of device performance is limited.

To illustrate the preferred embodiment, the opposing sidewalls (301) are illustrated as having a parabolic taper W (Z) along the propagation axis Z,

(Equation 1) Here, W ₀ is the width of the Z = 0 and Z = L _MMI of the MMI region, W ₁ is the width in the L _{MM I} / 2, Z is the propagation direction. This parabolic art can be manufactured relatively easily.

The access waveguides (305, 309) are arranged such that their outer ends coincide with the ends of the MMI region. The angle of the access waveguide is set to match the local taper angle at the end of the MMI region. By tilting the access waveguide in this manner, the tilt of the input image (305) will be approximately along a coordinate system that matches the end wall of the tapered MMI region. Z This, in combination with the tapered portion does not become discontinuous at the position of L _{MM I} / 2 shown, for example, in FIG. 2
= L _MMI / 2 Minimize the phase change caused by the existing discontinuous changes resembling a triangular linear taper. Besse, Gini, Bachmann and Melchior's "New 2 x 2
and 1x3 Multimode Interference Couplers With Free Selection of P
ower Splitting Ratios ", Journal of Lightwave. Vol. 14 pp. 2286-92, 1996. In the absence of the discontinuities such as Besse shown in FIG. 2, the imaging performance of the straight sidewall device is substantially maintained by the present invention because the width is tapered. That is, although the sidewalls of the structure are curved, the intensity distribution exhibits imaging performance similar to that of a linear MMI device of the type shown in FIG. 1 along the length of the device.

In the embodiment shown in FIG. 3, the tapered portions of both sidewalls are centered on the centerline of the propagation axis.
It is shown as symmetrical about the center. Similarly, this tapered portion is Z = L _MMI / 2 is symmetrical about a center line drawn perpendicular to the propagation axis. Therefore
, The differential of the taper becomes zero along the propagation axis in the multimode region,
That is, it has a single pole where dW (Z) / dZ = 0. 2 for this single pole
The bending symmetry of the piece is such as hyperbolic taper, elliptical taper, cosine taper, etc.
Formed by various simple functions that can be easily introduced into such MMIs
Can be. Of course, the tapered portion has a continuous derivative, and the average width of the MMI region is one.
If the layers become shorter and enjoy the benefits of the present invention, an asymmetric inward facing
Can be used. Such an asymmetric taper or taper with multiple poles
Device does not achieve the optimal power splitting function,
Another function is to act as a splitter and achieve the advantage of reducing the average width of the MMI region.
It can be used to perform functions based on MMI. Similarly, one side wall
Is a straight line, and only the side wall facing this side wall has an inward taper to
It is also possible to narrow the width and enjoy the advantages of the present invention.

Additionally, for the embodiment shown in FIG. 3, the width of the MMI region is the same at Z = 0 and Z = L _MMI . While this configuration is optimal for a 3-dB power splitter, varying the width at the input and output ends of the MMI region is useful in other MMI-based devices such as mode expanders or spot size converters. These devices can achieve the benefits of the present invention by forming a continuously curved taper to reduce the average width W _MMI .

[0028] For example, a device according to the invention shown in FIG. 3, as a function of changes in _{dQ = (W o -W l)} / W o become normalized width, split ratio, the length and total transmittance Can be characterized. The split ratio is defined as the power output from one of the access waveguides divided by the sum of the output power from both output waveguides.
Thus, for a full 3-dB power splitter, the split ratio of both output states is 0
. It becomes 5. The transmittance is the ratio of the total power of the input signal to the total power of the input signal. Therefore, in the case of a device having no transmission loss, the total transmittance ratio is 1. The length reduction is the total length of the MMI region of the curved device according to the present invention divided by the length of the MMI region of the corresponding device having straight side walls. All these characteristics of the device according to the invention can be shown as a function of dQ. If dQ = 0, the device is a normal linear side device. Taper is dQ
Becomes closer to 1 and opposing side walls contact each other at a point where dQ is 1.

FIG. 4 shows a division ratio (402) of the 3-dB MMI device shown in FIG. Solid circles (404) and solid squares (406) indicate the ratios for the cross and bar output access waveguides, respectively. As can be seen, the power splitting function of the 3-dB splitter, ie, split ratio = 0.5, is maintained over a wide range of dQ. Of course,
As will be apparent to those skilled in the art, dQ is essentially constrained by the requirement that the MMI region be wide enough to support the large number of mode lights required to maintain the interference-based imaging performance of the MMI device. receive. Similarly, as shown in FIG. 4, the total transmittance ratio indicated by the black triangle (408) is maintained at 0.8 or more up to dQ = 0.5 in the case of the 3-dB device shown in FIG. I have. further,
As shown in FIG. 5, which shows the normalized length of the MMI region as a function of dQ, the length indicated by the line connecting the circles has been reduced by almost half at dQ = 0.4. .

In this regard, it is useful to compare the functionality according to the invention with known prior art techniques that use a straight triangular taper to introduce phase in power transfer between states of the output waveguide. In this regard, for example, Besse, Gini, Bachmann, cited earlier.
And Melchior. The purpose of the triangular discontinuous taper (202) in FIG. 2 is to introduce a phase change to cause a change in the power split ratio as a function of dQ, unlike a straight sidewall device. As is clear from FIG. 4, the division ratio of the output state of the triangular discontinuous taper device represented by the white circle (410) and the white square (412) diverges as dQ increases. In contrast to this, the object of the present invention is not to use the phase change effect, which is the object of the prior art discontinuous taper device shown in FIG. Reducing the size of the MMI device while maintaining the imaging characteristics,
An object is to prevent optical coupling between access waveguides, improve manufacturing tolerances, and improve transmission quality.

As noted above, the advantages of the present invention are not limited to reducing the size of MMI-based devices. For example, the primary design objective of the device is not to achieve the shortest possible length, but to eliminate transmission losses in the access waveguide using the present invention and to improve the manufacturing width tolerance ΔW. is there. According to the present invention, Z = 0 in FIG. 3 can be obtained without sacrificing the overall length due to the taper forming effect.
These results can be achieved because the device can be provided with a wider width at the end of the device and Z = L _MMI . The wider end width of the MMI region allows a wider access waveguide to be used, further reducing transmission loss and improving the manufacturing tolerances of the width of the MMI region. In addition, the wider end width allows the access waveguides to be spaced further apart, which reduces optical coupling or power transfer between the access waveguides, as well as lithographic gap filling. Manufacturing defects due to various problems can be additionally reduced. The degree of miniaturization desired conflicts with the other improvement benefits achieved by utilizing the reduced average width of the sloping sidewalls and MMI regions according to the present invention. Is a design choice.

Of course, the invention is not limited to the 2 × 2 coupler described above. The benefits achieved by reducing the average width of the MMI region by utilizing a smoothly continuous taper according to the present invention are generally applicable to couplers based on an N × M MMI. Here, N is the number of access waveguides on the input side, and M is the number of access waveguides on the output side.

For example, FIG. 6 shows a 4 × 4 MMI coupler according to the present invention. FIG. 6 shows a 4 × 4 power splitter. The same self-imaging principle is applied to the MMI region (601), and in general, the N images of the input optical signal appear first, so the required length L _MMI of the multi-mode region is given by the following equation: Given by L _MMI = 4n _eff W _MMI ² / Nλ Accordingly, the length of these devices decreases with the number of outputs or the number N of images. The reduction in length obtained by using the parabolic taper shown is 1 / χ, where:

(Equation 2) Here, γ ² = W _o / W _l −1.

As shown in FIG. 6, the device 10 has a parabolic taper (603) similar to the taper of the device shown in FIG. 3, which is symmetric about the axis of propagation or the Z-axis. And symmetric about a center line orthogonal to the Z axis at Z = L _MMI / 2. The device has four input access waveguides (607) and four output access waveguides (609), the angle of the access waveguides (611) being the Z of the tapered MMI region (601). = 0 and Z = L The image is set so that an image tilted substantially along a coordinate system that is conformal to the end wall at the _MMI is formed. In the case of a parabolic taper, the tilt angle θ is obtained by the following form: θ = tan ⁻¹ (4y · dΩ / L _MMI ) where y is the position from the center of the access waveguide, and dΩ is the change in the normalized width described above, that is, dΩ = (W _o −W _o). ) / W _o . The widths W _o at both ends of the MMI region are equal to each other, and each taper is Z = L _{MMI at} which the device width is W _1.
/ 2 has a single pole.

FIG. 7 shows the device table shortening (701) compared to a linear device for various taper shapes as a function of dΩ (705) for a typical N × N device.
The total transmittance (703) is also shown as a function of dΩ (705) for 4 × 4 devices. The length reduction (701) is normalized to the length of the linear device, ie dΩ = 0. The radiator taper (707) shows a length reduction using an elliptical taper (708) and a consinsoidal shaped taper (711). Levy Scaromozzino and Osgood's "Length R" for calculating taper length reduction.
eductiom of Tapered N × N MMI Device ”, IEEE Photonics Techno
See logies Letters, Expected Publication Date June 1998. Each taper results in a length reduction of approximately 50% at dΩ = 0.4. Similarly, the total transmission curve (713) shows that the taper is stable at 80% or more until dΩ ≒ 0.5.

FIG. 8 shows the intensity distribution at the end of the MMI region of dΩ = 0.4 of the 4 × 4 MMI device as shown in FIG. As can be seen, the power splitting function is substantially maintained, having a power approximately equal to the four intensity peaks (802) associated with the four output waveguides (609). This corresponds to the divergence power curve (410, 4) shown in FIG.
It can be compared with the results when a discontinuous putty is used according to Besse and Gigi apparent in 12).

Therefore, the MMI coupler configured according to the present invention can be expected to have a wide variety of applications in various N × N devices, and can maintain the power division function, reduce the size, and improve the transmittance. Improvements, improved manufacturing width tolerances, reduced optical coupling, and reduced lithographic buried defects can be expected.

Although the present invention has been described with reference to the above specific embodiments, various modifications and alterations of the above described embodiments may be made without departing from the scope of the present invention as defined by the appended claims. In particular, various modifications and changes are possible with respect to the shape of the inward taper.

[Brief description of the drawings]

FIG. 1 shows a conventional linear 2 × 2 MMI coupler in the form of a 3-dB power splitter with linear shaped sidewalls.

FIG. 2 shows a conventional 2 × 2 MMI coupler with a linear triangular taper with discontinuous derivatives used for variable image power distribution.

FIG. 3 shows a 2 × 2 MMI coupler of the present invention with inwardly curved tapered sidewalls used as a 3-dB power splitter.

FIG. 4 is a graph showing the total power transmission of a 2 × 2 MMI device according to the invention and a comparison between a 2 × 2 MMI power splitter of a conventional straight triangular taper device and a device according to the invention.

FIG. 5 is a graph showing a reduction in device length of a 2 × 2 MMI coupler implemented according to the present invention.

FIG. 6: 4 × 4M according to the invention with inwardly curved tapered side walls
3 shows an MI coupler.

FIG. 7 shows the length reduction for various tapers of an N × NMMI coupler as well as the total transmission of a 4 × 4 MMI coupler according to the present invention.

FIG. 8 shows approximately equal power distributions of four image outputs from the 4 × 4 coupler shown in FIG.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Robert Scarmozzino, Inventor, United States of America 10548 Montrose Lancaster Avenue 13 (72) Inventor Richard M. Osgood, Jr.

Claims (17)

[Claims] (A) at least one input access waveguide for inputting an input optical signal to a first end of the interference-based multi-mode coupler; and (b) a second input access waveguide of the interference-based multi-mode coupler. (C) coupling one or more input access waveguides to one or more output access waveguides; and (c) coupling one or more input access waveguides to one or more output access waveguides. A multi-mode region wherein the input optical signal propagates along the propagation axis from the first end to the second end and re-images on one or more output access waveguides. (I) the multimode region has two opposing side walls that define the width of the coupler at each point along the propagation axis; and (ii) at least one side wall of the multimode region opposes. To the side wall And the coupler has an average width along the propagation axis that is less than the average width when both sidewalls are straight, and (iii) the sidewall has a propagation axis. Multimode coupler based on smoothly continuous interference with continuous derivatives along. 2. The multimode coupler based on interference according to claim 2, wherein
An interference-based multimode coupler in which both sidewalls have a non-linear taper inward toward the opposing sidewall, and the taper of both sidewalls is symmetric about a centerline along the propagation axis. . 3. The multi-mode coupler according to claim 2, wherein:
An interference-based multi-mode coupler wherein the taper has a single pole in the multi-mode region with a derivative zero along the propagation axis. 4. The multimode coupler based on interference according to claim 2, wherein
An interference-based multi-mode coupler, wherein the coupler has equal widths at the first end and the second end. 5. The multi-mode coupler according to claim 3, wherein:
An interference-based multimode coupler, wherein the coupler has equal widths at the first end and the second end. 6. The multi-mode coupler according to claim 4, wherein:
An interference-based multi-mode coupler in which the taper of the two side walls is symmetric about a center line orthogonal to a propagation axis at an intermediate point between the first end and the second end. 7. The interference-based multi-mode coupler according to claim 5,
An interference-based multi-mode coupler in which the taper of the two side walls is symmetric about a center line orthogonal to a propagation axis at an intermediate point between the first end and the second end. 8. The multi-mode coupler based on interference according to claim 4, wherein
An interference-based multimode coupler, wherein the input access waveguide and the output access waveguide are coupled to a multimode region at an angle that matches a local taper angle at an end of the multimode region. 9. The multi-mode coupler based on interference according to claim 5, wherein
An interference-based multimode coupler, wherein the input access waveguide and the output access waveguide are coupled to a multimode region at an angle that matches a local taper angle at an end of the multimode region. 10. The multimode coupler based on interference according to claim 3, wherein said tapered shape is parabolic, hyperbolic, elliptical or cosinusoidal. 11. The multimode coupler according to claim 4, wherein said tapered shape is parabolic, hyperbolic, elliptical, or cosinusoidal. 12. The multimode coupler according to claim 1, wherein the mode light guided to the maximum curvature of the taper characterized by the second derivative of the taper along the propagation axis is substantially maintained. -Mode coupler based on interference set as follows. 13. An input access waveguide for inputting an optical signal to a first end, and (b) an output of two images of the input optical signal from a second end. (C) coupling the two input access waveguides to the two output access waveguides, wherein the input optical signal propagates along a propagation axis and Re-imaging as two images, wherein the images comprise a multi-mode region having half the intensity of the input optical signal; and (i) the multi-mode region has a width of the coupler along each point of the propagation axis. And wherein the width of the first end and the width of the second end are substantially equal, and (ii) the side walls are inwardly directed toward the opposing side walls. A symmetrical taper is formed with respect to the propagation axis, and this taper is continued along the propagation axis. A continuous curve having a function, multi-mode power splitter 2 × 2 based on interference single pole the derivative becomes zero along the propagation axis is present in the multi-mode region. 14. The power splitter according to claim 13, wherein the taper is symmetric about a center line orthogonal to a propagation axis at an intermediate point between the first end and the second end. Power splitter. 15. The power splitter according to claim 14, wherein the shape of the taper is parabolic, hyperbolic, elliptical, or cosinusoidal. 16. The power splitter of claim 13, wherein the input access waveguide and the output access waveguide are coupled to a multi-mode region at an angle that matches a local taper angle at an end of the multi-mode region. Power splitter. 17. The power splitter according to claim 13, wherein a maximum curvature of the taper, characterized by a second derivative of the taper along the propagation axis, is set such that guided mode light is substantially maintained. Power splitter.