Method and apparatus for switching an optical beam in an integrated circuit die

What is claimed is:

1. An apparatus, comprising: a first semiconductor substrate layer; an optical switching device disposed in the first semiconductor substrate layer, first and second optical ports disposed in the first semiconductor substrate layer, the first and second optical ports optically coupled to the optical switching device; a first optical confinement layer disposed proximate to the first semiconductor layer; a second semiconductor substrate layer disposed proximate to the first optical confinement layer, the first optical confinement layer disposed between the first and second semiconductor substrate layers; and an integrated circuit disposed in the second semiconductor substrate layer.

2. The apparatus of claim 1 wherein the integrated circuit is coupled to generate a signal coupled to be received by the optical switching device, the first optical port selectively optically coupled to the second optical port through the optical switching device in response to the signal.

3. The apparatus of claim 2 wherein the integrated circuit is disposed opposite the optical switching device across the first optical confinement layer.

4. The apparatus of claim 2 wherein the integrated circuit includes driver circuitry coupled to generate the signal, the driver circuitry disposed opposite the optical switching device across the first optical confinement layer.

5. The apparatus of claim 4 further comprising a signal line coupled to carry the signal from the driver circuitry to the optical switching device through the first optical confinement layer.

6. The apparatus of claim 2 wherein the integrated circuit comprises a processor.

7. The apparatus of claim 2 wherein the integrated circuit comprises an application specific integrated circuit (ASIC).

8. The apparatus of claim 2 wherein the integrated circuit comprises a coder-decoder circuit (CODEC).

9. The apparatus of claim 1 further comprising a charge region proximate to the optical switching device, the charge region modulated responsive to a signal coupled to be received by the optical switching device.

10. The apparatus of claim 9 wherein the signal is coupled to control a charge distribution of the charge region across the optical switching device, an interference pattern of the optical switching device to be controlled responsive to the charge distribution.

11. The apparatus of claim 1 further comprising a second optical confinement layer disposed proximate to the first semiconductor layer, the first semiconductor layer disposed between the first and second optical confinement layers.

12. The apparatus of claim 1 wherein the integrated circuit comprises metal oxide semiconductor (MOS) circuitry disposed in the second semiconductor substrate.

13. The apparatus of claim 1 further comprising a third optical port disposed in the first semiconductor substrate layer, the third optical port optically coupled to the optical switching device, the first optical port selectively optically coupled to the third optical port through the optical switching device in response to the signal.

14. The apparatus of claim 1 wherein the optical switching device comprises a phase array having plurality of trench capacitors disposed in the first semiconductor substrate.

15. The apparatus of claim 1 wherein the optical switching device comprises a thermal heater disposed in the first semiconductor substrate.

16. The apparatus of claim 15 wherein the thermal heater comprises a resistor disposed in the first semiconductor substrate.

17. The apparatus of claim 1 wherein the optical switching device comprises a current injector disposed in the first semiconductor substrate.

18. The apparatus of claim 1 wherein the optical switching device comprises a P-N junction disposed in the first semiconductor substrate.

19. A method, comprising: directing an optical beam through a first optical port into a second semiconductor substrate layer; directing the optical beam along the semiconductor substrate layer through an optical switching device disposed in the second semiconductor substrate layer; selectively directing the optical beam to a second optical port in response to a signal coupled to be received by the optical switching device; confining the optical beam from exiting a first side of the second semiconductor substrate layer with a first optical confinement layer disposed proximate to the first side semiconductor substrate layer; and operating an integrated circuit disposed in a first semiconductor substrate layer, the first semiconductor substrate layer disposed proximate to the first optical confinement layer, the first optical confinement layer disposed between the first and second semiconductor substrate layers.

20. The method of claim 19 further comprising confining the optical beam from exiting a second side of the second semiconductor substrate layer with a second optical confinement layer disposed proximate to the second side semiconductor substrate layer, the first side of the semiconductor substrate layer opposite the second side of the semiconductor substrate layer.

21. The method of claim 19 further comprising selectively directing the optical beam to a third optical port in response to the signal coupled to be received by the optical switching device.

22. The method of claim 19 wherein the optical beam is directed through the optical switching device through an optical path disposed in the second semiconductor substrate layer, the method further comprising confining the optical beam from exiting the optical path with first and second optical confinement regions disposed in the second semiconductor substrate layer proximate to the optical path, the optical path disposed between the first and second optical confinement regions.

23. The method of claim 19 wherein operating the integrated circuit includes generating the signal with the integrated circuit.

24. The method of claim 23 further comprising routing the signal from a driver circuit of the integrated circuit to the optical switching device through a signal line routed through the first optical confinement layer, the driver circuit disposed in the first semiconductor substrate layer opposite the optical switching device across the first optical confinement layer.

25. An apparatus, comprising: means for directing an optical beam into a first semiconductor substrate layer; means for selectively directing the optical beam to a means for transmitting the optical beam from the first semiconductor substrate layer in response to a signal; means for confining the optical beam from exiting the first semiconductor substrate layer prior to being directed to the means for transmitting the optical beam from the first semiconductor layer; and integrated circuit means disposed in a second semiconductor layer, the second semiconductor layer disposed proximate to the means for confining the optical beam from exiting the first semiconductor substrate layer, the means for confining the optical beam from exiting the first semiconductor substrate layer disposed between the first and second semiconductor substrate layers.

26. The apparatus of claim 25 wherein the integrated circuit means includes means for generating the signal disposed in the second semiconductor substrate layer.

27. The apparatus of claim 26 further comprises means for routing the signal from the means for generating the signal to the means for selectively directing the optical beam.

28. The apparatus of claim 25 wherein the means for transmitting the optical beam from the first semiconductor layer comprises a plurality of optical ports, wherein in one of the plurality of optical ports is selected responsive to the signal.

29. The apparatus of claim 25 wherein the means for selectively directing the optical beam comprises a means for modulating a charge distribute across an optical switching device disposed in the first semiconductor substrate layer.

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the switching signals and, more specifically, the present invention relates to switching or routing optical signals.

2. Background Information

The need for fast and efficient optical switches is increasing as Internet data traffic growth rate is overtaking voice traffic pushing the need for optical communications. Two commonly found types of optical switches are mechanical switching devices and electro-optic switching devices.

Mechanical switching devices generally involve physical components that are placed in the optical paths between optical fibers. These components are moved to cause switching action. Micro-electronic mechanical systems (MEMS) have recently been used for miniature mechanical switches. MEMS are popular because they are silicon based and are processed using somewhat conventional silicon processing technologies. However, since MEMS technology generally rely upon the actual mechanical movement of physical parts or components, MEMS are generally limited to slower speed optical applications, such as for example applications having response times on the order of milliseconds.

In electro-optic switching devices, voltages are applied to selected parts of a device to create electric fields within the device. The electric fields change the optical properties of selected materials within the device and the electro-optic effect results in switching action. Electro-optic devices typically utilize electro-optical materials that combine optical transparency with voltage-variable optical behavior. One typical type of single crystal electro-optical material used in electro-optic switching devices is lithium niobate (LiNbO.sub.3).

Lithium niobate is a transparent, material that exhibits electro-optic properties such as the Pockels effect. The Pockels effect is the optical phenomenon in which the refractive index of a medium, such as lithium niobate, varies with an applied electric field. The varied refractive index of the lithium niobate may be used to provide switching. The applied electrical field is provided to present day electro-optical switches by external control circuitry.

Although the switching speeds of these types of devices are very fast, for example on the order of nanoseconds, one disadvantage with present day electro-optic switching devices is that these devices generally require relatively high voltages in order to switch optical beams. Consequently, the external circuits utilized to control present day electro-optical switches are usually specially fabricated to generate the high voltages and suffer from large amounts of power consumption. In addition, integration of these external high voltage control circuits with present day electro-optical switches is becoming an increasingly challenging task as device dimensions continue to scale down and circuit densities continue to increase.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitation in the accompanying figures.

FIG. 1 is a side view illustration of one embodiment of an optical switch including optical confinement layers in accordance with the teachings of the present invention.

FIG. 2 is a top view illustration of one embodiment of optical confinement regions included in an optical switch that is biased to modulate a phase of a portion of an optical beam in accordance with the teachings of the present invention.

FIG. 3 is a top view illustration of another embodiment of optical confinement regions included in an optical switch that is biased to modulate a phase of a portion of an optical beam in accordance with the teachings of the present invention.

FIG. 4 is a side view illustration of another embodiment of an optical switch including optical confinement layers in accordance with the teachings of the present invention.

FIG. 5 is a side view illustration of one embodiment of an optical switch combined with integrated circuitry disposed in a semiconductor die having optical confinement layers in accordance with the teachings of the present invention.

FIG. 6 is a top view illustration of one embodiment of optical confinement regions included in an optical switch including a phase array to selectively direct an incident optical beam to one of a plurality of output ports in accordance with the teachings of the present invention.

FIG. 7 is a top view illustration of another embodiment of optical confinement regions included in an optical switch including a phase array having an asymmetric geometry to selectively direct an incident optical beam to one of a plurality of output ports in accordance with the teachings of the present invention.

DETAILED DESCRIPTION

Methods and apparatuses for confining an optical beam in an optical switch are disclosed. In the following description numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

In one embodiment of the present invention, a semiconductor-based optical switch or router is provided in a fully integrated solution on a single integrated circuit chip. One embodiment of the presently described optical switch includes optical confinement layers and/or regions and can be used in a variety of high bandwidth applications including multi-processor, telecommunications, networking or the like. In one embodiment, the presently described optical modulator includes an array of trench capacitors disposed in a silicon semiconductor substrate layer. In one embodiment, the optical confinement layers and/or regions are employed to help confine an optical beam to pass through the array of trench capacitors. The array of trench capacitors may also be referred to as a phase array in accordance with the teachings of the present invention. Charge in the array is modulated by the trench capacitors to switch an optical beam directed through the array in response to a signal. In one embodiment, the control circuitry used to generate the signal is integrated in the same die as the array. Thus, in one embodiment the array and the control circuitry are fully integrated on the same integrated circuit chip. In one embodiment, the optical beam is switched by the array selectively attenuating the optical beam. In another embodiment, the optical beam is switched by selectively modulating the phase of at least a portion of the optical beam.

In one embodiment, a one-dimensional array is formed with the trench capacitors in the semiconductor substrate layer. In another embodiment, a two-dimensional array is formed with the trench capacitors in the semiconductor substrate layer. In one embodiment, a phase array including uncharged and selectively modulated charged regions is provided by the array trench capacitors. In one embodiment, the interference intensity pattern caused by the phase array is modulated in response to a signal. For instance, by selectively biasing individual trench capacitors in one embodiment of the phase array, the charge distribution across the phase array can be controlled by the signal in one embodiment of the present invention.

As a result, the amount of phase modulation of different portions of the optical beam passing through different portions the phase array is controlled by the signal in one embodiment. A resulting interference occurs between the phase modulated portions and non-phase modulated portions of the optical beam. The interference among the different portions of the optical beam results in an interference intensity pattern of the phase array, which may be controlled by the signal in one embodiment of the present invention. By adjusting the interference intensity pattern of the phase array, an incident optical beam is selectively directed to one of a plurality of output ports in accordance with the teachings of the present invention.

FIG. 1 is a side view illustration of one embodiment of an optical switch 101 including optical confinement layers in accordance with the teachings of the present invention. In one embodiment, optical switch 101 is a controlled collapse chip connection (C4) or flip chip packaged integrated circuit die coupled to package substrate 109 through ball bonds 107. As can be appreciated by those skilled in the art, ball bonds 107 provide more direct connections between the internal integrated circuit nodes of optical switch 101 and the pins 121 of package substrate 109, thereby reducing inductance problems associated with typical wire bond integrated circuit packaging technologies. In one embodiment, the internal integrated circuit nodes of optical switch 101 are located towards the front side 104 of optical switch 101. Another characteristic of flip chip packaging is that full access to a back side 102 of optical switch 101 is provided. It is appreciated that in another embodiment, optical switch 101 is not limited to being mounted in a flip chip packaged configuration. In other embodiments, packaging technologies other than flip chip packaging may be employed in accordance with the teachings of the present invention such as for example but not limited to wire bond packaging or the like.

In one embodiment, the optical switch 101 of the present invention includes an optical switching device 134 including an array of trench capacitors including trench capacitor 135 and trench capacitor 137, as illustrated in FIG. 1. In one embodiment, trench capacitors 135 and 137 include polysilicon disposed in a semiconductor substrate layer 103 of optical switch 101. In one embodiment, semiconductor substrate layer 103 includes silicon. As illustrated in FIG. 1, one embodiment of optical switch 101 includes an insulating region 153 disposed between the polysilicon of trench capacitor 135 and the semiconductor substrate layer 103. Similarly, an insulating region 155 is disposed between the polysilicon of trench capacitor 137 and the semiconductor substrate layer 103.

In one embodiment, a signal 129 and a signal' 131 are coupled to be received by trench capacitors 135 and 137, respectively, of optical switching device 134. In one embodiment, signal 129 and signal' 131 are generated by control circuitry on the integrated circuit die of optical switch 101. In one embodiment, the control circuit generating signal 129 and signal' 131 is disposed in semiconductor substrate layer 103 outside of the optical path between optical input port 149 and optical port 151. In another embodiment, signal 129 and signal' 131 are generated by control circuitry external to the integrated circuit die of optical switch 101. In one embodiment, signal 129 and signal' 131 are coupled to be received by trench capacitors 135 through conductors 119 and 121, which are disposed in an optical confinement layer 105 of optical switch 101. In one embodiment, optical confinement layer 105 is an insulating layer and includes a dielectric layer of optical switch 101.

In one embodiment, signal 129 and signal' 131 are a plurality of signals separately coupled to be received by the trench capacitors 135 and 137 in optical switching device 134. For example, in one embodiment, signal 129 and signal' 131 are the same signals having opposite polarities. In another embodiment, signal 129 and signal' 131 are the same signals having the same polarities. In yet another embodiment, signal 129 and signal' 131 are separate signals coupled to capacitors across the array to control or modulate a charge distribution of free charge carriers across the array of trench capacitors 135 and 137.

As illustrated in FIG. 1, one embodiment of optical switch 101 includes an optical input port 149 and an optical output port 151 disposed in or optically coupled to semiconductor substrate layer 103 on different sides of the array of trench capacitors 135 and 137 of optical switching device 134. In one embodiment, an optical beam 111 is directed optical input port 149 and through semiconductor substrate layer 103 to the array of trench capacitors 135 and 137 of optical switching device 134. In one embodiment, optical beam 111 is directed into optical input port 149 through an optical fiber or the like. As mentioned, in one embodiment, semiconductor substrate layer 103 includes silicon, trench capacitors 135 and 137 include polysilicon and optical beam 111 includes infrared or near infrared laser light. As known to those skilled in the art, silicon is partially transparent to infrared or near infrared light. For instance, in one embodiment in which optical switch 101 is utilized in telecommunications, optical beam 111 has an infrared wavelength of approximately 1.55 or 1.3 micrometers.

As will be discussed, optical beam 111 is switched by the array of trench capacitors 135 and 137 of optical switching device 134. A switched optical beam 127 is then directed from the array of trench capacitors 135 and 137 through semiconductor substrate layer 103 to optical output port 151. In one embodiment, switched optical beam 127 is directed from optical output port 151 through an optical fiber or the like. It is appreciated that in other embodiments (not shown), optical beam 111 and switched optical beam 127 may enter and/or exit semiconductor substrate layer 103 through back side 102 and/or front side 104 in accordance with the teachings of the present invention.

In one embodiment, optical switch 101 includes an optical confinement layer 157 disposed proximate to semiconductor substrate layer 103. Thus, semiconductor substrate layer 103 is disposed between optical confinement layer 157 and optical confinement layer 105. In one embodiment, optical confinement layer 157 is an insulating layer. In particular, optical energy or light from optical beam 111 or switched optical beam 127 is reflected from the interfaces between semiconductor substrate layer 103 and optical confinement layer 157 or optical confinement layer 105. For example, light from optical beam 111 will have an angle of incidence .theta. relative to the interface between semiconductor substrate layer 103 and optical confinement layer 157 or optical confinement layer 105. For purposes of this disclosure, an incident angle .theta. is the angle that an optical beam makes with an imaginary line perpendicular to a surface at the point of incidence. In the embodiment depicted in FIG. 1, optical beam 111 or switched optical beam 127 is deflected off the interface between semiconductor substrate layer 103 and optical confinement layer 157 or optical confinement layer 105 because of total internal reflection.

In one embodiment, optical confinement layer 157 and optical confinement layer 105 include silicon oxide or the like and have an index of refraction of approximately n.sub.oxide =1.5 and semiconductor substrate layer 103 includes silicon and has an index of refraction of approximately n.sub.Si =3.5. In order to have total internal reflection of optical beam 111 or switched optical beam 127, the incident angle .theta. of optical beam 111 or switched optical beam 127 relative to the interface between semiconductor substrate layer 103 and optical confinement layer 157 or optical confinement layer 105 satisfies the following relationship:

As a result of the total internal reflection, optical beam 111 is in one embodiment is confined to remain with semiconductor substrate layer 103 using optical confinement layer 157 and optical confinement layer 105 until switched optical beam 127 exits through optical output port 151.

In one embodiment, optical switch 101 is constructed from a silicon-on-insulator (SOI) wafer. For instance, during manufacture, a known SOI wafer is provided including a semiconductor substrate layer 159, optical confinement layer 157 and semiconductor substrate layer 103. Trench capacitors 135 and 137 of optical switching device 134 are then formed in semiconductor substrate layer 103. In one embodiment, trench capacitors are fabricated to be approximately 1-2 .mu.m deep. It is appreciated of course that in other embodiments, trench capacitors 135 and 137 may have different depths in accordance with the teachings of the present invention. Next, optical confinement layer 105 is formed with conductors 119 and 131 providing accesses to trench capacitors 135 and 137. Afterwards, ball bonds 107 and package substrate 109 are added.

FIG. 2 is a top view illustration of one embodiment of optical confinement regions 261 and 263 included in an optical switch 201 that is biased such that an optical beam 211 is switched in accordance with the teachings of the present invention. As illustrated, an array of trench capacitors 235, 236, 237 and 238 are disposed in a semiconductor substrate layer 203. Insulating regions 253, 254, 255 and 256 are disposed between the semiconductor substrate layer 203 and polysilicon of trench capacitors 235, 236, 237 and 238, respectively. An optical path is disposed between optical input port 249 and optical output port 251. In one embodiment, optical fibers or the like are optically coupled to optical input port 249 and optical output port 251.

In one embodiment, optical confinement regions 261 and 263 are disposed along the sides of optical path between optical input port 249 and optical output port 251. As shown in the embodiment depicted in FIG. 2, optical confinement regions 261 and 263 are disposed a distance D away from insulating regions 253, 254, 255 and 256. In one embodiment, D is a distance greater than or equal to zero. Accordingly, in another embodiment in which D is equal to zero, optical confinement regions 261 and 263 are adjacent to insulating regions 253, 254, 255 and 256. In one embodiment, the optical confinement regions 261 and 263 include insulative material such as for example oxide and semiconductor substrate layer 203 includes for example silicon. As a result, optical beam 211 and switched optical beam 227 are confined to remain within the semiconductor substrate layer 203 until exiting through optical output port 251. In one embodiment, optical confinement layers, similar to for example optical confinement layer 157 and optical confinement layer 105 of FIG. 1, are also disposed along the "top" and "bottom" of the optical path is disposed between optical input port 249 and optical output port 251. These optical confinement layers are not shown in FIG. 2 for clarity.

In the depicted embodiment, trench capacitors 235, 236, 237 and 238 are biased in response to signal voltages such that the concentration of free charge carriers in charged regions 239, 240, 241 and 242 of the array of trench capacitors is modulated. In one embodiment in which D is greater than zero, an optical beam 211 is directed through semiconductor substrate layer 203 such that a portion of optical beam 211 is directed to pass through the modulated charge regions 239, 240, 241 and 242 and a portion of optical beam 211 is not directed to pass through the modulated charge regions 239, 240, 241 and 242. As a result of the modulated charge concentration in charged regions 239, 240, 241 and 242, optical beam 211 is switched resulting in switched optical beam 227 being directed from the array of trench capacitors through semiconductor substrate layer 203.

In one embodiment, semiconductor substrate layer 203 is doped to include free charge carriers. In one embodiment, semiconductor substrate layer 203 is n type doped silicon and the free charge carriers are electrons. In another embodiment, semiconductor substrate layer 203 is p type doped silicon and the free charge carriers are holes. In one embodiment, the polysilicon of trench capacitors 235, 236, 237 and 238 is n type doped polysilicon and the free charge carriers are electrons. In another embodiment, the polysilicon of trench capacitors 235, 236, 237 and 238 are p type doped polysilicon and the free charge carriers are holes.

In one embodiment, the free charge carriers attenuate optical beam 211 when passing through semiconductor substrate layer 203. In particular, the free charge carriers attenuate optical beam 211 by converting some of the energy of optical beam 211 into free charge carrier energy.

In another embodiment, the phase of the portion of optical beam 211 that passes through the charged regions 239, 240, 241 and 242 is modulated in response to the signal. In one embodiment, the phase of optical beam 211 passing through free charge carriers in charged regions 239, 240, 241 and 242 is modulated due to the plasma optical effect. The plasma optical effect arises due to an interaction between the optical electric field vector and free charge carriers that may be present along the propagation path of the optical beam 211. The electric field of the optical beam 211 polarizes the free charge carriers and this effectively perturbs the local dielectric constant of the medium. This in turn leads to a perturbation of the propagation velocity of the optical wave and hence the refractive index for the light, since the refractive index is simply the ratio of the speed of the light in vacuum to that in the medium. The free charge carriers are accelerated by the field and also lead to absorption of the optical field as optical energy is used up. Generally the refractive index perturbation is a complex number with the real part being that part which causes the velocity change and the imaginary part being related to the free charge carrier absorption. The amount of phase shift .phi. is given by

with the optical wavelength .lambda. and the interaction length L. In the case of the plasma optical effect in silicon, the refractive index change .DELTA.n due to the electron (.DELTA.N.sub.e) and hole (.DELTA.N.sub.h) concentration change is given by: ##EQU1##

where n.sub.0 is the nominal index of refraction for silicon, e is the electronic charge, c is the speed of light, .di-elect cons..sub.0 is the permittivity of free space, m.sub.e * and m.sub.h * are the electron and hole effective masses, respectively, b.sub.e and b.sub.h are fitting parameters.

In one embodiment, the amount of phase shift .phi. of some portions of optical beam 211 passing through the free charge carriers of charged regions 239, 240, 241 and 242 is approximately .pi./2. In one embodiment, the phase of a portion of optical beam 211 not passing though the free charge carriers of charged regions 239, 240, 241 and 242, i.e. passing through uncharged regions, is relatively unchanged. In one embodiment, a resulting interference occurs between the phase modulated portions and non-phase modulated portions of optical beam 211 passing through the array of trench capacitors 235, 236, 237 and 238. In one embodiment in which D is equal to zero, there is no portion of optical beam 211 not passing though the free charge carriers of charged regions 239, 240, 241 and 242 as optical confinement regions 261 and 263 confine optical beam 211 to pass through charged regions 239, 240, 241 and 242.

It is noted that optical switch 201 has been illustrated in FIG. 2 with four trench capacitors 235, 236, 237 and 238. It is appreciated that in other embodiments, optical switch 201 may include a greater or fewer number of trench capacitors in accordance with the teachings of the present invention with the number of trench capacitors chosen to achieve the required phase shift. In particular, the interaction length L discussed in connection with Equation 2 above may be varied by increasing or decreasing the total number of trench capacitors 235, 236, 237 and 238 in optical switching device 134 of optical switch 201.

FIG. 3 is a top view illustration of one embodiment of optical confinement regions 361 and 363 included in an optical switch 301 that is biased such that an optical beam 311 is switched in accordance with the teachings of the present invention. As illustrated, one embodiment of optical switch 301 includes an optical switching device 334 having a trench capacitor 335 disposed in a semiconductor substrate layer 303. An insulating region 353 is disposed between the polysilicon of trench capacitor 335 and semiconductor substrate layer 303. In one embodiment, trench capacitor 335 is one of a plurality or array of trench capacitors disposed in semiconductor substrate layer 303. An optical path is disposed between optical input port 349 and optical output port 351. In one embodiment, optical fibers or the like are optically coupled to optical input port 349 and optical output port 351.

In one embodiment, optical confinement regions 361 and 363 are disposed along the sides of optical path between optical input port 349 and optical output port 351. As shown in the embodiment depicted in FIG. 3, optical confinement regions 361 and 363 are disposed a distance D away from insulating region 353. In one embodiment, D is a distance greater than or equal to zero. In one embodiment, the optical confinement regions 361 and 363 include insulative material such as for example oxide and semiconductor substrate layer 303 includes for example silicon. As a result, optical beam 311 and switched optical beam 327 are confined to remain within the semiconductor substrate layer 303 until exiting through optical output port 351. In one embodiment, optical confinement layers, similar to for example optical confinement layer 157 and optical confinement layer 105 of FIG. 1, are also disposed along the "top" and "bottom" of the optical path is disposed between optical input port 349 and optical output port 351. These optical confinement layers are not shown in FIG. 3 for clarity.

In the depicted embodiment, trench capacitor 335 is biased in response to a signal such that the concentration of free charge carriers in charged regions 339 is modulated. In one embodiment, an optical beam 311 is directed through semiconductor substrate layer 303 such that a portion of optical beam 311 is directed to pass through the modulated charge regions 339 and a portion of optical beam 311 is not directed to pass through the modulated charge region 339. As a result of the modulated charge concentration in charged region 339, optical beam 311 is switched resulting in switched optical beam 327 being directed from trench capacitor 335 through semiconductor substrate layer 303. In an embodiment in which D is equal to zero, there is no portion of optical beam 311 not passing through modulated charge region 339.

In one embodiment, the phase of the portion of optical beam 311 that passes through the charged regions 339 is modulated in response to the signal due to the plasma optical effect discussed above. As can be observed from Equation 2 above, one way to increase the phase shift .phi. in optical beam 311 is to increase the interaction length L of the charged region 339. In one embodiment, an increase interaction length L is provided by trench capacitor 335 by providing an increased dimension L, as illustrated in FIG. 3.

FIG. 4 is a side view illustration of another embodiment of an optical switch 401 including