Cross-Reference to Related Application

This application is being filed on September 12, 2017 as a PCT International Patent Application and claims the benefit of U.S. Patent Application Serial No.

62/393,463, filed on September 12, 2016, the disclosure of which is incorporated herein by reference in its entirety.

Background of the Invention

The present invention is generally directed to optical communications, and more specifically to active optical switch systems that use electro-wetting on dielectric (EWOD) active optical switches.

Optical fiber networks are becoming increasingly prevalent in part because service providers want to deliver high bandwidth communication and data transfer capabilities to customers. As optical networks become more complex, it has become increasingly important to manage optical signals in the network. Many optical signal management functions, such as redirecting signals to bypass faulty components, or opening new channels to facilitate the addition of more users of the network, can be accomplished using active optical switches, such as electro-wetting on dielectric (EWOD)-activated optical switches. Such active optical switches are based on the principles of microfluidics: two fluids with different refractive indices, wherein at least one fluid is a liquid, are moved in an adiabatic waveguide coupler. Depending on the location of the fluids relative to the waveguide coupler, the coupler switches between two states, either facilitating or prohibiting the transition of a propagating optical signal from one waveguide to another.

It is important that the properties of the fluids used in an EWOD optical switch are selected to be compatible and so that an EWOD optical switch can operate effectively and efficiently.

Summary of the Invention

An embodiment of the invention is directed to an active optical switch system that has a substrate having at least a first waveguide and a waveguide-fluid coupling area and a fluid channel above the substrate. A first liquid, having a first refractive index, is within the fluid channel. A second liquid, immiscible with the first liquid and having a second refractive index, is also within the fluid channel. The second refractive index is different from the first refractive index by at least 0.18. At least one of the first and second liquids is selectively movable relative to the waveguide-fluid coupling area so as to affect an effective refractive index of the first waveguide. The optical switch system also includes a fluidic driving mechanism for moving at least one of the first and second liquids within the fluid channel. The fluidic driving mechanism has at least one electrode positioned to apply an electric field to at least the first fluid in the fluid channel. The second liquid has a dynamic viscosity less than 50 cP, the value of dynamic viscosity being determined at 25 °C. The first liquid is a polar liquid having a relative permittivity, ε _Γ , greater than 20. The first and second liquids each have a boiling point higher than 70 °C.

The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.

Brief Description of the Drawings

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 schematically illustrates an embodiment of an active optical switch system according to an embodiment of the present invention;

FIG. 2 schematically illustrates a cross-sectional view through a portion of an active optical switch system according to an embodiment of the present invention;

FIG. 3 A shows absorbance of ethylene glycol as a function of wavelength;

FIG. 3B shows absorbance of deuterated ethylene glycol as a function of wavelength;

FIG. 4A shows absorbance of diphenyl sulfide as a function of wavelength;

FIG. 4B shows absorbance of diphenyl sulfide, deuterated diphenyl sulfide and a mixture of non-deuterated and deuterated diphenyl sulfide;

FIG. 5 A shows absorbance of hydroxy propylene carbonate as a function of wavelength;

FIG. 5B shows absorbance of deuterated hydroxy propylene carbonate as a function of wavelength; FIG. 5C shows absorbance of a mixture of deuterated hydroxy propylene carbonate and deuterated water as a function of wavelength;

FIG. 6A presents data relating to the optical performance of an EWOD switch, according to an embodiment of the present invention using a combination of triphenyl sulfide and hydroxy propylene carbonate, in the bar state; and

FIG. 6B presents data relating to the optical performance of an EWOD switch, according to an embodiment of the present invention using a combination of triphenyl sulfide and hydroxy propylene carbonate, in the cross state.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Detailed Description

The present invention is directed to systems, devices, and methods that can provide benefits to optical communication networks.

An exemplary embodiment of an active optical switch 100 is schematically illustrated in FIG. 1. The active optical switch 100 incorporates a first waveguide 102 and a second waveguide 104. The first and second waveguides 102, 104 are situated physically closer to one another in a waveguide-light coupling region 106, a region where light propagating along one of the waveguides 102, 104 may couple to the other waveguide 104, 102. Whether light couples between the waveguides 102, 104 depends on the effective refractive index experienced by the light as it propagates along the waveguides 102, 104. The effective refractive index can be altered by positioning a fluid of greater or lesser refractive index close to the waveguide-light coupling region 106 and the waveguide-fluid coupling region 108, discussed further below.

In many embodiments, the active optical switch includes two fluids that are moveable to change the state of the switch. The figure shows a first fluid 110 positioned over the waveguide-light coupling region 106 and the waveguide-fluid coupling region 108. A second fluid 112 is shown generally filling the remaining space of the fluid channel 114. The first and second fluids 110, 112 may be in either a liquid or gaseous phase. The first fluid 110 has a first refractive index and the second fluid 112 has a second refractive index, different from the first refractive index. The first and second fluid 110, 112 may move within the fluid channel 114, so for example, the first fluid 110 may move away from waveguide-light coupling region 106 and waveguide-fluid coupling region 108 to the location shown as 110a, with the second fluid 112 generally filling the remaining space in the fluid channel 114. One or more of the inner surfaces of the fluid channel 114 may be coated with anti -wetting coatings 116, 118 to assist in controlling the position of first and second fluids 110, 112 with respect to the waveguide-light coupling region 106 and waveguide-fluid coupling region 108.

In the illustrated embodiment, an optical signal transmitted into the first waveguide 102 is coupled to the second waveguide 104 when the first fluid 110 is positioned close to the waveguide-light coupling region 106 and the waveguide-fluid coupling region 108. This is referred to as the switch's "cross state." An optical signal transmitted into the first waveguide 102 is maintained in the first waveguide 102 when the first fluid 110a is positioned away from the waveguide-light coupling region 106 and the waveguide-fluid coupling region 108, and instead the second fluid 112 is positioned near coupling regions 106, 108. This is referred to as the switch's "bar state." Microfluidic optical switches have previously been described, for example in U.S. Provisional Patent Application No. 62/094,506, "Integrated Optical Switching and Splitting for Optical Networks," filed on December 19, 2014, in U.S. Provisional Patent Application No. 62/116,784, entitled "Remote Control and Power Supply for Optical Networks," filed on February 16, 2015, and in WO 2015/092064A1, "Adiabatic Coupler," published on June 25, 2015, all of which are incorporated herein by reference.

A cross-sectional view through a portion of an exemplary embodiment of an active optical switch system 200 is schematically illustrated in FIG. 2. In this embodiment, optical fluids are moved in a fluid channel relative to waveguides using the technique of electro-wetting. A first fluid 210 and a second fluid 212 are disposed within a fluid channel 202 formed between two structures 204, 206. In the illustrated embodiment, the first fluid 210 and the second fluid 212 are both liquids. The first fluid 210 has a first refractive index and the second fluid 212 has a second refractive index, different from the first refractive index. The first structure 204 is provided with a common electrode 208, insulated from the fluid channel 202 by a first dielectric layer 214, which provides at least partial electrical insulation between the common electrode 208 and the fluids 210, 212 and the fluid channel 202. A first anti-wetting layer 216 may be deposited on the first dielectric layer or substrate 214 to facilitate movement of the fluids 210, 212 in the fluid channel 202.

The second structure 206 is provided with multiple electrodes 218, 220 that can be activated with an applied voltage independently of each other. A fluidic driving mechanism, generally 222, comprises the common electrode 208 and the independently addressable electrodes 218, 220. Only two independently addressable electrodes 218, 220 are shown in the illustrated embodiment, but it will be appreciated that other embodiments of the invention may include a larger number of independently addressable electrodes. Multiple independently addressable electrodes 218, 220 may be located in the first structure 204, while the common electrode may be located in the second structure 206. In alternative embodiments, it may not be necessary to insulate each electrode from the fluids in an EWOD-type optical switch, which may require only one electrode being insulated from the fluids. Other additional embodiments may have the independent addressable electrodes and a common electrode located in the same substrate, for example the first structure 204. Alternative embodiments may include only independently addressable electrodes, without a common electrode incorporated into the active optical switch system, wherein the independently addressable electrodes are located, for example, in the first structure 204.

A second dielectric layer or substrate 224, having an upper surface 226, at least partially insulates electrodes 218, 220 from the fluids 210, 212 and the fluid channel 202. In the illustrated embodiment, the surface 226 is also the bottom surface of the fluid channel 202. A second anti-wetting layer 228 may be deposited on the second dielectric layer or substrate 224, for example on the shared surface 226, to facilitate movement of fluids 210, 212 in the fluid channel 202.

The second substrate 224 contains a first waveguide 230 and a second waveguide

232. An etched region 234 of the second substrate 224 above the second waveguide 232 exposes the second waveguide 232 at or close to the upper surface 226 of the second substrate 224, on which the second anti -wetting layer 228 may be deposited. The etched region 234 defines a waveguide-fluid coupling region 224a of the second substrate 224, in which the refractive index of the fluid located above the second waveguide 232 can affect the propagation constant of light passing along the second waveguide 232. The first waveguide 230 is located away from the etched region 234 of the second substrate 224 and away from the waveguide-fluid coupling region 224a, remaining isolated within the second substrate 224 so that the refractive index of the fluid above the first waveguide 230 has substantially no impact on the propagation constant for light passing along the first waveguide 230.

In the illustrated embodiment, the first fluid 210 has a relatively higher refractive index than the second fluid 212. The first fluid 210 is located within the fluid channel 202 and in the etched region 234, so that the relatively higher refractive index of the first fluid 210 affects the effective refractive index experienced by light propagating along the second waveguide 232. According to the illustrated embodiment, light can couple between the first and second waveguides 230, 232 when the first fluid 210 is in the etched region 234. In other words, when the first fluid 210 is in the etched region 234, the switch 200 is in the cross state. In another switch state, when the first fluid 210 is outside the etched region 234, and the second fluid 212, having a relatively lower refractive index is in the etched region 234, the effective refractive index experienced by light propagating along the second waveguide 232 is changed, preventing coupling of light between the waveguides 230, 232 and the switch is in the bar state. In alternative embodiments, the first fluid may have a lower refractive index than the second fluid, so that the first fluid may induce the switch to assume the cross state when the first fluid is in the etched region. Alternative embodiments may include a first fluid of relatively higher refractive index than the second fluid, and which induces a bar state when in the etch region, and vice versa.

The electro-wetting (EW) effect arises when the contact angle of a liquid is changed due to an applied electrical potential difference. In the illustrated embodiment, when an electric field is generated between, for example, electrodes 208, 220, the surface tension of liquid 210 lying between the electrodes 208 and 220, can be reduced, allowing it to "wet" the surface it contacts. As in the embodiment illustrated in FIG. 2, because the EW effect is applied to the first liquid 210 separated from electrodes 208, 218, 220, by dielectric layers 214, 224, this configuration is referred to as electro-wetting on dielectric (EWOD). As discussed above, only one electrode need be insulated from the fluids of the switch to qualify as an EWOD-type switch.

In the illustrated embodiment, the fluidic driving mechanism 222 selectively applies electric potentials to the electrodes 208, 218, 220 of optical switch 200 to move the fluids 210, 212 inside the fluid channel 202. For example, in a configuration (not shown) where fluid 210 is above the first waveguide 230, i.e. not in the etched region 234, voltages may be applied to the second electrode 220, together with common electrode 208, and then the first electrode 218. Such activation of electrodes 218, 220 may result in the first fluid 210 moving from a location above the first waveguide 230 to the location shown in FIG. 2, above the second waveguide 232 and in the etched region 234. The movement of the first fluid 210 causes corresponding movement of the second fluid 212 inside the fluid channel 202. In this way the state of the optical switch system 200 can be selected to be in a bar or cross state. In other embodiments electrodes may be provided only on one side of the fluid channel.

The use of the EW effect to move liquid droplets is well known, and the use of microfluidics in the control of optical waveguide devices has been described in

WO2015/092064A1, "Adiabatic Coupler," filed on December 21, 2014, incorporated herein by reference, in U.S. Provisional Patent Application NO. 62/094,506, "Integrated Optical Switching and Splitting for Optical Networks," filed on December 19, 2014, and in U.S. Provisional Patent Application No. 62/116,784, entitled "Remote Control and Power Supply for Optical Networks," filed on February 16, 2015, both of which have been incorporated by reference. But it will be appreciated that other conformations and configurations of electrode and fluid or liquid can be used to move fluids 210, 212. It will further be appreciated that such approaches can be used to move two or more liquids. For example, if a channel contains two immiscible liquids, separated at an inter-liquid interface, movement of one of the liquids via the EW effect can result in both liquids being moved in the channel. The second liquid can be moved along the channel by the EW forces acting on the first liquid, even though the second liquid does not itself exhibit EW behavior. For example, liquids that respond well to EW typically are polar in nature, but the second liquid may be non-polar, yet still be moved as a result of an EW force applied via a polar liquid. The EW technique can also be used to move liquid droplets around a network of microchannels, so long as electrodes are suitably positioned along the different channels.

The inventors have found that the following liquid characteristics are desirable for efficient and effective operation of EWOD optical switches. Unless otherwise stated, the liquid properties are given at 25 °C.

i) The liquids should be substantially transparent over the wavelength range of interest. In many cases, optical switches are used for optical communications signals that fall in the wavelength range 1260 nm - 1650 nm, thus the liquids should not introduce substantial optical losses. It has been determined that a loss of around 3 dB/cm is an acceptable level of optical loss for EWOD optical switches. The two liquids should be immiscible. This is a requirement because it is important that the two liquids are kept separate from each other so as to be able to control the positions of the two liquids relative to the optical waveguides of the switch. If the liquids are miscible, then the positions of the two liquids relative to the waveguides cannot be controlled as well, reducing the effectiveness of the switch. A useful measure of miscibility is based on the Hansen solubility parameters, which are known characteristics for different fluids, 5 _d , due to dispersion forces, δ _ρ , due to dipolar intermolecular forces, and 5 _h , due to hydrogen bonds, where the parameters are each generally measured in MPa° ⁵ . The difference between the Hansen parameters for two liquids, AHSPiP, can be calculated from:

AHSPiP = (4(5 _dl - δ^) ² + (δ _ρΐ - δ _ρ2 ) ² + (6hi - 5h ₂ ) ² ) ^1/2 where the subscripts 1 and 2 refer to the first and second liquids respectively. The two liquids are immiscible if AHSPiP, is higher than a certain threshold value, with the threshold being dependent on which nonpolar fluid is being used. For example, when using diphenyl sulfide (DSP) or triphenyl sulfide (TSP) as the nonpolar fluid, it has been found that a difference of AHSPiP > 19 is required for the liquids to be immiscible: a value of AHSPiP = 18.14

(between acetonitrile and diphenyl sulfide) is insufficient to prevent mixing of the two liquids.

The difference in refractive index, n, at the design wavelength between the first liquid, nl, and the second liquid, n2, is preferably at least 0.18 and more preferably is at least 0.2. A larger refractive index difference, Δη (= |nl-n2|), permits more efficient and more compact switch architecture. The refractive index of each liquid is dependent on the wavelength of operation.

The relative permittivity, ε _Γ , of the polar liquid is preferably greater than 20, more preferably greater than 40, even more preferably greater than 80. Higher values of relative permittivity are generally related to a liquid being more polar and more susceptible to the electro-wetting effect.

The temperature range over which the optical switch may be required to operate is from -40 °C to +70 °C. Accordingly, the liquids should remain liquid over the temperature range, having a melting point (m.p.) < 40 °C and a boiling point (b.p.) > 70 °C. vi) The dynamic viscosity of the ambient liquid, i.e. that liquid which is more prevalent in the fluid channel, should be relatively low so as to permit the liquids to flow easily within the fluid channel under an applied electro-wetting force. In many applications of configurations of EWOD optical switch, the nonpolar liquid is the ambient fluid. The viscosity of the ambient liquid should preferably be less than 50 cP, more preferably less than 30 cP and even more preferably less than 20 cP, where the value of viscosity is determined at 25 °C. One suitable category of high refractive index, non-polar liquid is the polyphenyl sulfides, for example diphenyl sulfide (DPS) and triphenyl sulfide (TPS). Table I lists a number of different low refractive index, polar liquids that can be considered for use with a polyphenyl sulfide, along with a number of polyphenyl sulfides, including DPS, TPS and Santolube SL-5267. Each of the low refractive index, polar liquids has a AHSPiP > 19 when compared with DPS. The last three lines of the table show the same parameters for DPS, TPS and Santolube SL5267, a commercially available grade of TPS. References herein to TPS are to czs-TPS and not to tmns-TPSm which is solid at room temperature.

Table I: Properties of Selected Liquids

The values of refractive index, n, in the table are measured at a wavelength of 590 nm, while the values of relative permittivity, ε _Γ , are measured at DC. The refractive index difference, Δη, is the refractive index difference between the liquid and DPS.

Ethylene glycol (EG) and n-methylformamide do not meet the melting point limit of being less than -40 °C, but may be suitable where the operating temperature range is not as large, e.g. for applications indoors.

Methanol has a density that is 40% less than the density of DPS, making its density matching properties less desirable than some other liquids. In addition, methanol has a boiling point less than the 70 °C desired upper limit, and the value of ε _Γ = 30 gives it less desirable electro-wetting properties than other liquids. Ethanol has a density similar to that of methanol and a lower value of ε _Γ than methanol, although its temperature properties are suitable to a desired operating range of from -40 °C to +70 °C. Formamate and n- methyl formamate do not have the temperature properties suitable for the desired operating range, and the Δη of formamate is on the lower side of the desired range. HPC has desirable temperature characteristics, but its Δη with DPS, while still acceptable, is lower than the preferred value of 0.2.

Consequently, the low refractive index, polar liquids listed in Table I that have the most favorable characteristics for use in an EWOD optical switch, include HPC, HPC + H ₂ 0 and EG.

The commercial grade of Santolube SL-5267 is not suitable for use in an EWOD optical switch because its viscosity is too high, at 79 cP, and it cannot be easily moved within the fluid channel under the electro-wetting force. A chemical analysis of SL-5267 revealed that it contained a mixture of polyphenylsulfides, containing 3, 4 and 5 phenyl rings. The presence of the 4 and 5 phenyl ring components likely increased the viscosity beyond acceptable levels. The TPS reported in Table I was synthesized with care taken to avoid the presence of components having more than three phenyl rings. It is preferred that the viscosity of the ambient liquid, in this example the non-polar liquid, is less than 50 cP, more preferably less than 30 cP and even more preferably less than 20 cP.

Consequently, of the three high refractive index, nonpolar liquids shown in Table I,

DPS and TPS are the most suitable for use in an EWOD optical switch. Optical absorption of the light by the liquids in an EWOD optical switch contribute to the overall insertion losses of the switch. It is, therefore, desirable to reduce the optical absorption of light by the liquids used in the optical switch. For the wavelengths for which an EWOD switch is used it is, therefore, desirable that the absorbance of the liquids used in the EWOD switch be around 3.5 dB/cm or less, preferably 3 dB/cm or less.

FIG. 3 A shows the absorbance spectrum for EG over the range of 400 nm to 2000 nm. The absorbance is low over all wavelengths longer than 400 nm with the exception of a peak of 8 dB/cm at around 1150 nm, a small, broad peak around 1400 nm and a sharp high peak starting at about 1600 nm. Thus, EG has an absorbance below 3 dB/cm for most commonly used communications wavelengths, including 850 nm, 1310 nm and 1550 nm. However, the absorbance in the 1625-1650 nm range is high, making EG less suitable for communications at this wavelength.

It has previously been reported that deuteration of the liquids used in an EWOD optical switch can result in the movement of certain absorption bands to longer wavelengths, see "Integrated Optical Switches using Deuterated Liquids for Increased Bandwidth," filed on February 4, 2016, provisional application no. 62/291,300.

Deuteration is the replacement of a hydrogen atom in the molecule with a deuterium atom. In some cases, a molecule can be partially deuterated, in which case at least some of the hydrogen atoms in the molecule are replaced by deuterium atoms. In other cases, a compound can be fully deuterated, in which case the all the hydrogen atoms of the molecule are replaced by deuterium atoms. FIG. 3B shows the absorbance spectrum of deuterated EG, where the -OH (hydroxy) groups have been replaced by -OD (deuteroxy) groups. The major absorption edge at around 1600 nm in EG has been moved beyond 1800 nm through deuteration, and the absorbance is at, or below, 3 dB/cm for all wavelengths from 400 nm - 1750 nm. Thus, deuterated EG is suitable for use in an EWOD optical switch over the wavelength range 1250 nm - 1650 nm.

FIG. 4A shows the absorbance of DPS over the range of 400 nm - 2000 nm. The absorbance is low over all wavelengths longer than 400 nm with the exception of a peak of 7 dB/cm at around 1130 nm, a small, broad peak around 1400 nm and a sharp, high peak starting at about 1600 nm. Thus, DPS has an absorbance below 3 dB/cm for several commonly used communications wavelengths, including 850 nm, 1310 nm and 1550 nm. However, the absorbance in the 1625-1650 nm range is high, making DPS less suitable for communications at this wavelength. FIG. 4B shows the absorbance of three different DPS-based liquids. The first, curve 402, is the absorbance curve for DPS, as shown in FIG. 4A. The second, curve 404, is the absorbance curve for fully deuterated DPS, called DPS-dlO (referring to deuteration at the 10 available hydrogen sites around the two phenyl rings). The absorbance for DPS- dlO is less than 3 dB/cm for wavelengths up to about 1500 nm, where there is a peak at 4.4 dB/cm. The third absorbance curve, curve 406, shows the absorbance for a mixture of DPS and DPS-dlO in a volume ratio 28:72 DPS:DPS-dl0, with absorbance less than 3.3 dB/cm for wavelengths up to 1650 nm.

Since the preferred wavelengths for fiber communication include 850nm, 1310 nm, 1490nm and 1550 nm, wavelengths DPS for which the absorbance of DPS is less than 3 dB/cm, DPS is suitable for use in an EWOD optical switch operating at these wavelengths. DPS has a high absorbance at 1650 nm, however, which makes it less desirable for operation at wavelengths up to 1650 nm. The mixture of DPS:DPS-dl0 has an absorbance of less than 3.3 dB/cm up to wavelengths greater than 1650 nm, making this liquid a more suitable liquid for use in an EWOD operating at wavelengths up to 1650 nm.

The absorbance spectrum of TPS is similar to that of DPS and, likewise, the absorbance of fully deuterated TPS, TPS-dl4, is like that of deuterated DPS, DPS-dlO.

FIG. 5 A shows the absorbance spectrum of UPC over the range 400 nm - 2000 nm. It demonstrates significant absorbance, e.g. above 5 dB/cm, for wavelengths higher than 1400 nm, so it is suitable for low-loss use in EWOD optical switches operating at wavelengths less than 1400 nm, e.g. 1310 nm. FIG. 5B shows the absorbance spectrum for deuterated UPC, HPC-dl, where the hydroxy group has been deuterated. The absorbance for this liquid is less than 5 dB for wavelengths up to about 1640 nm

(absorbance at 1650 nm is 6.1 dB/cm), and 3.1 dB/cm at a wavelength of 1410 nm. Thus, deuterated UPC is suitable for low-loss use in EWOD switches operating at the common wavelength ranges up to 1600 nm.

FIG. 5C shows an absorbance spectrum for HPC-dl, curve 502, and for deuterated water, D ₂ 0, curve 504. The figure also shows the absorbance of a mixture of HPC-dl and D ₂ 0, in a volume ratio of 1 : 1, curve 506. The mixture of HPC-dl and D ₂ 0 demonstrates an absorbance below 3 dB/cm for all wavelengths in the range up to about 1640 nm, and is 4.3 dB/cm for 1650 nm. Thus the mixture of HPC-dl and D ₂ 0 is suitable for a low loss EWOD optical switch that operates up to 1640 nm. Examples

EWOD switches have been demonstrated using the following pairs of liquids:

i) DPS and HPC

ii) DPS + (HPC + H ₂ 0) (1 : 1)

iii) DPS + EG

iv) TPS and HPC

v) TPS + (HPC + H ₂ 0) (1 : 1)

vi) TPS + EG

Exemplary results obtained from example iv), an EWOD optical switch using TPS and HPC are presented in FIGs. 6 A and 6B. In each case the graph includes a diagram showing the respective switch configuration. FIG. 6A shows a switch in the bar state, with light propagating from the upper input port to the upper output port and from the lower input port to the lower output port. FIG. 6A shows that, over the range 1500 nm - 1600 nm, the switch in the bar state introduced a loss close to 0 dB for the bar ports, e.g. when a signal was input to the upper input port, the signal out of the upper output port was about 0 dB down from the input signal. The transmission loss was in the range of 40 dB - 50 dB for the cross ports, e.g. when a signal was input to the upper input port, the signal at the lower output port was about 40 dB - 50 dB down from the input signal.

FIG. 6B shows a switch in the cross state, with light propagating from the upper input port to the lower output port and from the lower input port to the upper output port. FIG. 6B shows that, over the range 1500 nm - 1600 nm, the switch in the cross state introduced a loss close to 0-1 dB for the cross ports, e.g. when a signal was input to the upper input port, the signal out of the lower output port was about 0-1 dB down from the input signal. The transmission loss was in the range of 12 dB - 30 dB for the bar ports, e.g. when a signal was input to the upper input port, the signal at the upper output port was about 12-30 dB down from the input signal.

In general larger refractive index differences resulted in reduced cross-talk between output ports. For example, when the same, low-index polar liquid is used, TPS produces improved cross-talk compared to a switch using DPS, since TPS has a higher refractive index than DPS and so the refractive index difference between the two liquids in the switch is higher.

Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the present specification. The claims are intended to cover such modifications and devices. For example, different mixtures of liquids can be used in addition to those described herein, including different ratios of components, and different mixture components. In addition, liquids may be deuterated to different degrees than those discussed. Furthermore, in addition to the mixtures discussed herein where the non-polar liquid has a relatively high refractive index and the polar liquid has a relatively low refractive index, the fluid combination may include a non-polar liquid with a relatively low refractive index and a polar liquid with a relatively high refractive index.

As noted above, the present invention is applicable to fiber optical communication and data transmission systems. Accordingly, the present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims.