US20100165351A1

US20100165351A1 - Silicon photonic waveguide biosensor configurations

Info

Publication number: US20100165351A1
Application number: US12/451,608
Authority: US
Inventors: Dan-Xia Xu; Adam Densmore; Andre Delage; Pavel Cheben; Siegfried Janz
Original assignee: Individual
Current assignee: National Research Council of Canada
Priority date: 2007-05-21
Filing date: 2008-04-09
Publication date: 2010-07-01
Also published as: CA2601836C; US7778499B2; CA2601836A1; EP2167945A4; US20080292236A1; CA2687917A1; WO2008141417A1; EP2167945A1

Abstract

Methods and devices relating to sensors and sensor blocks for use in detecting and monitoring molecular interactions. A silicon waveguide sensing element is provided along with a layer of silicon. A silicon oxide layer is also provided between the waveguide element and the layer of silicon. The sensing element is adjacent to an aqueous solution in which the molecular interactions are occurring. A light beam travelling in the silicon waveguide creates an evanescent optical field on the surface of the sensing element adjacent to the boundary between the sensing element and the aqueous medium. Molecular interactions occurring on this surface affect the intensity or the phase of the light beam travelling through the waveguide by changing the effective refractive index of the medium. By measuring the effect on the intensity, phase, or speed of the light beam, the molecular interactions can be detected and monitored in real time. Various configurations using this sensor technology is also disclosed.

Description

FIELD OF THE INVENTION

The present invention relates to sensor technology. More specifically, the present invention relates to sensors for detecting and quantifying molecular interactions by determining how much of an effect these molecular interactions have on characteristics of light passing through a waveguide adjacent an aqueous medium where these interactions are occurring.

BACKGROUND TO THE INVENTION

The recent increase in interest in and funding for the biochemical and pharmaceutical fields has created a need for more sensitive sensors that can detect and quantify molecular interactions. The detection of these molecular interactions determine whether chemical and biological processes are at work and, as such, are key to finding new and more effective pharmaceuticals.
Unfortunately, current biosensor technology suffers from a fragility and scarcity of the equipment. Current sensor technology, such as surface plasmon resonance (SPR), is quite well-known but the equipment requires delicate handling by technicians. Furthermore, such current technologies have sensitivities that are less then desirable. With SPR, the sensitivity of the equipment is limited by the short propagation length of the plasmon.
There is therefore a need for methods and devices that mitigate if not overcome the shortcomings of the prior art.
Specifically, there is a need for techniques and devices which are easy to implement, robust, and whose sensitivity is not determined by the short propagation lengths of plasmons.

SUMMARY OF THE INVENTION

The present invention provides methods and devices relating to sensors and sensor blocks for use in detecting and monitoring molecular interactions. A silicon waveguide sensing element is provided along with a layer of siliconA silicon oxide layer is also provided between the waveguide element and the layer of silicon. The sensing element is adjacent to an aqueous solution in which the molecular interactions are occurring. A light beam travelling in the silicon waveguide creates an evanescent optical field on the surface of the sensing element adjacent to the boundary between the sensing element and the aqueous medium.
Molecular interactions occurring on this surface affect the intensity or the phase of the light beam travelling through the waveguide by changing the effective refractive index of the medium. By measuring the effect on the intensity, phase, or speed of the light beam, the molecular interactions can be detected and monitored in real time. Various configurations in which the sensor can be used, such as in a ring resonator or a Mach-Zehnder interferometer, are also illustrated.
In one aspect, the present invention provides a sensor for use in detecting molecules in a liquid or gas medium, the sensor comprising:

- a substrate layer,
- a light waveguide sensor element adjacent said medium
- a lower cladding layer between said sensor element and said substrate layer
- wherein
- molecular interactions at the waveguide surface affect at least one characteristic of light travelling through said waveguide sensor element.

In another aspect, the present invention provides a method for detecting molecular interactions in a medium using a sensor having a light waveguide sensor element adjacent said aqueous medium, the method comprising:

- a) determining characteristics of light prior to said light entering said sensor element
- b) passing light through said sensor element
- c) determining characteristics of light after it has exited said sensor element
- d) comparing results of steps a) and c) to determine if changes in characteristics of said light occurred
- e) in the event said changes in characteristics occurred, measuring said changes
- wherein a presence of molecular interactions in said medium affect at least one characteristic of said light.

In a further aspect, the present invention provides an optical sensor block for use in detecting molecules in a liquid or gas medium, the sensor block comprising:

- a group of sensors comprising at least two sensor elements wherein each sensor element comprises
  - a substrate layer
  - a light waveguide sensor adjacent said medium
  - a lower cladding layer between said waveguide sensor and said substrate layer
  - wherein
  - molecular interactions at the waveguide sensor surface affect at least one characteristic of light travelling through said waveguide sensor
  - light travelling through said waveguide sensor is for eventual reception by an optical detector.

Another aspect of the invention provides an optical sensor block for use in detecting molecules in a liquid or gas medium, the sensor block comprising:

- a Mach-Zehnder interferometer having a first and a second arm, said first arm being a sensor arm having an optical sensor element, said optical sensor element comprising:
  - a substrate layer
  - a light waveguide sensor adjacent said medium
  - a lower cladding layer between said waveguide sensor and said substrate layer
  - wherein
- molecular interactions at the waveguide sensor surface affect at least one characteristic of light travelling through said waveguide sensor
- light travelling through said waveguide sensor is for eventual reception by an optical detector.

A further aspect of the invention provides a sensor for use in detecting molecules in a liquid or gas medium, the sensor comprising:

- a substrate layer,
- a light waveguide sensor element adjacent said medium
- a lower cladding layer between said sensor element and said substrate layer
- wherein
- molecular interactions at the waveguide surface affect at least one characteristic of light travelling through said waveguide sensor element
- and wherein said sensor element is configured as a ring resonator.

In another aspect, the present invention provides a sensor for use in detecting molecules in a liquid or gas medium, the sensor comprising:

- a substrate layer,
- a light waveguide sensor element adjacent said medium
- a lower cladding layer between said sensor element and said substrate layer
- wherein
- molecular interactions at the waveguide surface affect at least one characteristic of light travelling through said waveguide sensor element
- and wherein said sensor element is configured as one arm of a Mach-Zehnder interferometer.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be described with reference to the accompanying drawings, wherein:

FIG. 1 is an isometric view of a sensor according to one aspect of the invention;

FIG. 2 is a front cut-away view of the sensor of FIG. 1 illustrating the core of the waveguide;

FIG. 3 is a side cut-away view of the sensor of FIG. 1 illustrating the direction of propagation of light travelling in the waveguide and the evanescent optical field produced by such light;

FIG. 4 illustrates the positioning of a molecular layer on a surface of the sensor of FIG. 1;

FIG. 5 is a side cut-away view of the sensor of FIG. 1 with a sensor window;

FIG. 6A illustrates a configuration of a sensor in which the silicon dioxide layer is provided as pillars supporting the waveguide;

FIG. 6B illustrates a top-down view of a configuration of the sensor which can be used as a ring resonator;

FIG. 7 illustrates a sensor configuration in which the sensor can be used as a microdisk resonator;

FIG. 8 illustrates a sensor configuration with dual arms;

FIG. 9 shows a configuration with a spiral arm;

FIG. 10 illustrates a sensor configuration using a coupler with four waveguide arms;

FIG. 11 shows a ring configuration for the sensor;

FIG. 12 a-FIG. 12 d illustrate four closer views of the ring configuration of FIG. 11;

FIG. 13 shows a configuration with dual ring sensors;

FIG. 14 illustrates multiple ring sensor configurations;

FIG. 15 illustrates the sensor configuration of FIG. 14 terminating with a loop mirror;

FIG. 16 illustrates a Mach-Zehnder configuration for the sensor;

FIG. 17 illustrates the configuration of FIG. 16 with the addition of a modulator;

FIG. 18 illustrates a Mach-Zehnder configuration for the sensor terminating with a photodetector array;

FIG. 19 schematically details multiple Mach-Zehnder configured sensors;

FIG. 20A-20B illustrates two different Mach-Zehnder configuration sensors;

FIG. 21A-FIG. 21C illustrate three sensors which use an unbalanced Mach-Zehnder configuration with a reduced temperature sensitivity;

FIG. 22 shows a Mach-Zehnder interferometer sensor comprising a waveguide section with a large group index for sensitivity enhancement;

FIG. 23 illustrates a 1×N addressable sensor array;

FIG. 24 illustrates a sensor array which use vertically coupled input and output beams;

FIG. 25 illustrates a sensor array which uses two multiplexer/demultiplexers.

DETAILED DESCRIPTION

Referring to FIG. 1, a sensor 10 according to one aspect of the invention is illustrated. The sensor 10 has an optical waveguide 20 (a sensor element) on top of a silicon dioxide layer 30. The silicon dioxide layer 20 (a lower cladding layer) is sandwiched between the waveguide 20 and a silicon substrate 40.
Referring to FIG. 2, an end cut-away view of the sensor 10 is illustrated. In use, from FIG. 2, a solution 50 (which may be water based) is adjacent the waveguide 20. The 50 contains the chemical or biochemical materials whose interactions are to be monitored or detected.
The sensor detects molecular interactions (or the presence of specific molecules) by having light passed through the sensor. The sensor detects the binding of specific, target molecules to receptor molecules on the waveguide surface. By detecting this binding, the presence of the target molecules is determined. The receptor molecules are previously attached (perhaps as a layer) to the waveguide surface. As an example, an antibody can be fixed to the sensor surface (the waveguide surface) to functionalize the antibody for detecting the presence of the corresponding antigen.
Referring to FIG. 3, a side-cutaway view of the sensor is illustrated. The sensor 20 operates by detecting the effect of target molecules binding to the waveguide surface on the characteristics of light as the light travels through the waveguide.
As is well-known in the art, especially to those well-versed in SPR technology, target molecules are detected when they bind to the surface 50A of the sensor. Light travelling in the waveguide 20 (in the direction 60 of propagation) produces an evanescent optical field 70 on the surface of the waveguide 20. The molecular interactions occurring near or at the surface 50A affect the refractive index of the liquid solution, thereby slowing down or delaying the light travelling through the waveguide. This effectively changes the speed and other characteristics of the light in the waveguide. Characteristics such as the intensity and the phase of the light are affected by the extent and number of molecular interactions on the surface of the waveguide.
Molecular interactions, such as the adsorption of molecules onto the sensor surface affect the speed of light as well as the attenuation of the light. The attenuation of the light also depends on the absorption cross section at the optical wavelength of the light travelling in the waveguide. As noted above, a phase change in the light in the waveguide may also be induced due to the adsorption of a molecular layer on the surface of the waveguide.
The changes in the characteristic of the light in the waveguide can be detected and measured by the use of well-known devices and techniques. Such devices as Mach-Zehnder interferometers and resonators may be used to measure these changes in characteristic. These same devices may be used to determine the initial characteristics of the light prior to their entering the sensor. Once the initial characteristics of the light are determined, these can be compared to the characteristics of the light after the light has passed through the sensor. The differences between these two sets of characteristics (such as speed of light, phase, etc.) would indicate the presence and number of molecular interactions detected.
Referring to FIG. 4, another cross-sectional view of the sensor is illustrated. As can be seen, the molecular layer 50B forms between the surface of the waveguide and the aqueous medium. Experiments have shown that sensor response increases with active sensor length and that sensor response increases with mode intensity at the perturbation location (i.e. the target molecule layer). The presence and number of target molecules can therefore be determined by sampling the characteristics (e.g. attenuation, phase, etc.) of the light travelling in the waveguide.
Experiments have shown that best results have been observed when silicon-on-insulator waveguides were used. Silicon photonic wire waveguides have been found to produce useful as the sensor elements in the sensor. For better results, a sensor window may be used to isolate the area where the waveguide core is exposed to the target molecules, to enable a comparison of the light travelling through the sensor waveguide with light travelling in an unexposed reference waveguide. Referring to FIG. 5, such a sensor window is illustrated. An isolation layer 80 isolates the evanescent optical field 70 from the aqueous medium 50 and the molecular interactions. A sensor window 90, an area in which the isolation layer is not present, exposes the evanescent optical field 70 to the medium 50 and thereby to the changed refractive index due to target-receptor molecule interactions. It should be noted that the isolation layer may be fabricated using well-known photosensitive polymer coatings normally used in the fabrication of semiconductor devices.
It should be noted that various configurations of the above noted sensor are possible. Referring to FIGS. 6A, 6B and 7, two different configurations are illustrated. FIGS. 6A and 6B illustrate a bridge configuration with the waveguide core being supported by pillars 80 of silicon oxide. This configuration allows the aqueous medium to surround the waveguide and thereby increase the surface area on which the molecular interactions can occur. Such a configuration can also be used to create a ring resonator as in FIG. 6B. In FIG. 7, a microdisk resonator can be configured using a single silicon oxide pillar 80 to support a microdisk waveguide sensor.
Experiments have also shown that better results have been achieved when the waveguides were thin as well as having a high contrast in terms of refractive index. Thus, better results were found when the contrast between the effective refractive index (N_eff) and the refractive index of the cladding was at a maximum. Also, it has been found that better results were achieved when the polarization of the light travelling in the waveguide was perpendicular to the active surface (the so-called TM mode). One material which produced acceptable results (thin waveguide, high index contrast, and TM mode) were silicon photonic wire waveguides. However, other materials may also provide equally acceptable results.
It should also be noted that the presence of a thin layer (i.e. the layer must be thinner than the extent of the evanescent field above the waveguide) of silicon dioxide between the waveguide and the medium containing the molecular interactions does not significantly degrade the performance (sensitivity) of the sensor. As such, a layer of silicon dioxide (i.e. glass) may be deposited on the waveguide.
Based on the above, silicon or other established glass bio-chip chemistries may be used in the production of the above noted sensor elements.
The above sensor technology may be used in a number of configurations. These configurations may enhance the results obtained by the sensor by increasing the area exposed to the material being sensed or the configurations may make it easier to interrogate the sensor.
The sensors may be arranged as a sensor block with multiple sensors. FIGS. 8-25 illustrate various embodiments of such a sensor block.
Referring to FIG. 8, the sensor block 500 has a single input 510 and a single output 520. Between these is a reference arm 530 and a sensor window 540. The reference arm 530 and the sensor window 540 are constructed by having the light waveguide element 550 configured as a single weaving pattern with each trace of the pattern being parallel to the other traces to result in a grid-like pattern of parallel lines, preferably as closely packed parallel lines. In weaving terminology, the pattern traced by the waveguide element would be the same as that traced by a weft yarn (or the “fill yarn” or “woof yarn”) in plain weaving. As can be seen from the figure, the single input 510 is split into two paths—one of which turns into the sensor window while the other turns into the reference arm. The outputs of the sensor window and of the reference arm then combine into the single output 520. The light waveguide sections in the sensor window are exposed to the material being sensed while the sections in the reference arm are not exposed to the material.
Referring to FIG. 9, the light waveguide sensor may be configured as a sensor block 600 with a sensor element arranged as a spiral 610. As can be seen from the figure, this sensor block arrangement has the same single input and output. At the end of the spiral may be placed a mirrored Bragg grating loop or similar device. The spiral section 610 is exposed to the material being sensed. The spiral section may be configured as a unifilar mirrored spiral.
The spiral section may also be configured as a bifilar spiral. Such arrangement obviates the need for a mirror and provides physically separated input and output waveguides.
Referring to FIG. 10, the sensitivity of the sensor can be amplified by using a resonator effect. A linear two-mirror resonator 620 is illustrated in FIG. 10. A coupler 630 couples four waveguides—an input waveguide 640, an output waveguide 650, a sensing window waveguide 660, and an optional shifter waveguide 670. As can be seen from the figure, the sensing window waveguide terminates at a mirror 675, for example a Bragg reflector, a metallic mirror, or a loop mirror. The optional phase compensator/shifter waveguide 670 also terminates in a similar mirror/reflector. The signal enters through the input 640 and is sensed through the sensing window 680 and is reflected back by the mirror/reflector 675. The signal exits via output 650.
Referring to FIGS. 11 and 12, the sensor block 703 may, again, have a single input 710 and a single output 720. The sensor element 730 in the sensor window 740 may be configured as a ring resonator with a multimode interference (MMI) coupler 750. One preferred configuration (with measurements) of the MMI coupler is illustrated in FIG. 12 b). The appearances of the ring resonator and of the coupler, as implemented in silicon, are shown in FIGS. 12 c) and d). In this configuration, the ring resonator structure would be exposed to the material being sensed as the structure would be within the sensor window.
Referring to FIG. 13, the ring resonator structure may be used in a variety of configurations. In FIG. 13, two ring resonators are placed side by side such that the output of resonator L1 becomes the input to resonator L2. In this configuration, the L1 resonator is inside a sensor window and, as such, is exposed to the material being sensed. The L2 resonator may be used as a reference to cancel out signal variations due to temperature. As is known, a single ring resonator will have a resonance wavelength that shifts with temperature as dλ/dT˜(L/m)(dN_eff/dT), where m is the ring order. However, the separation in wavelength resonances for two ring resonators of nearly the same ring path length will be significantly smaller—d(λ₁−λ₂)/dT˜((L1−L2)/m)(dN_eff)/dT). Opening a sensor window over one ring and covering the other ring to act as a reference and using the difference in resonance wavelength as the transduction signal may cancel out the transduction signal variations due to temperature.
Referring to FIG. 14, ring resonators may be used in other configurations. In FIG. 14, the sensor block 800 has a single input 810 and a single output 820 with ring resonators 830, 840, 850. Each ring resonator may be wavelength addressable such that each ring resonator only responds to a single wavelength or a specific range of wavelengths. Each ring resonator may be configured so that it has a specific resonance wavelength and each resonator can be individually monitored by measuring the wavelength shift of its resonance. Addressing and signal monitoring for each resonator may be done by sending only one light input at a time with the light having a specific wavelength to address a single resonator. The output 820 may then be measured by a detector 860 which may or may not be part of the sensor block. The detector 860 may be a photodetector if only one wavelength of light at a time is inputted into the sensor block. Alternatively, the detector 860 may be a spectrometer if a broad spectrum of light is inputted—the positions of all the resonances may be monitored if the spectrometer is used. Of course, each of the ring resonators in this configuration is in a sensor window and, as such, each resonator is exposed to the material being sensed.
Referring to FIG. 15, the results from a ring resonator configuration may be enhanced by passing the same light through the sensor twice. As can be seen from FIG. 15, instead of a detector at the end of the sensor block 900, a loop mirror 910 may be placed at the end of the output of sensor block. The loop mirror would reflect the output light and the light would then pass through the relevant ring resonator again. A circulator 920 would then redirect the returning sensor signal to the measuring optics and electronics.
Referring to FIG. 16, another configuration of a sensor block 1000 using the light waveguide technology explained above is illustrated. In this configuration, a single input is used and the input light is split between two arms of a Mach-Zehnder interferometer. One arm 1020 is used as a sensor window while the other arm 1030 is used as a reference arm.
The output of each arm is then joined into a single output 1040. As with the previous configurations, the section of the waveguide in the sensor window is exposed to the material being sensed. The other sections of the light waveguide are shielded from the material being sensed. In this configuration, if the two arms are designed to have precisely the same optical path length and the same average dN_eff/DT (with Neff being the effective index of the waveguide mode) the output of the Mach-Zehnder will be independent of temperature and wavelength. The sensor block will only respond to the molecular adsorption and index changes in the material over the sensor window.
The configuration in FIG. 16 may be adjusted to have an optical modulator in the reference arm. Such a configuration is illustrated in FIG. 17. In FIG. 17, the modulator 1050 modulates the effective index of the light signal at high frequency. By using lock-in or heterodyning techniques to measure the modulated component cf the Mach-Zehnder signal output, low frequency (e.g. 1/f) noise in the detector and optical source may be eliminated.
The ring resonator configuration and the Mach-Zehnder configuration may be combined into a single sensor block as in FIG. 18. The sensor block 1100 has a single input 1110, a reference arm 1120, and a signal arm 1130 with a ring resonator 1140 in the sensor window 1150. The output of both arms would be received by a 1×N MMI or star coupler 1160. This produces an interference pattern and this can be sampled directly by imaging the output plane of the MMI or sampled with appropriately placed waveguides 1170 with a photodetector array 1180. This interference pattern will shift as molecules adsorb on the light waveguide sensor or the fluid index of the material being sensed changes. As the interference pattern is the transduction signal, the sensor block response is independent of fluctuations of input light power.
The Mach-Zehnder configuration of the sensor block may be combined with other sensor blocks to arrive at an array of sensor blocks. Referring to FIG. 19, an array of sensor blocks is illustrated. In this array, each element of the array has a configuration similar to that illustrated in FIG. X8 in that each array element is a Mach-Zehnder interferometer with a modulator in the reference arm and a sensor window in the sensor arm. The only exception to this is the topmost array element—this array element does not have a sensor window and is used as a reference. The modulator bias of the topmost array element without the sensor window is adjusted to keep the output of the reference circuit constant. The output of every other sensor block circuit is adjusted with an identical bias so that drifts due to temperature and environmental effects are eliminated. The signal change is thus only due to molecular adsorption or fluid index change. It should be noted that while Mach-Zehnder interferometer configurations are used in FIG. 19, a similar configuration used ring resonators is also possible. For such a ring configuration, the topmost element is, again, devoid of a sensor window.
The Mach-Zehnder configuration may also be altered to arrive at other, useful sensor blocks. As an example, referring to FIGS. 20A and 20B, these configurations may be useful in reducing the number of fiber attachments. In both configurations, a mirror 1200 is used at the output of the Mach-Zehnder interferometer. In FIG. 20A, two mirrors are used—one at the end of each arm of the interferometer. In FIG. 20B, only one mirror 1200 is used after the combining of the outputs of each arm. In both cases, a circulator 1210 is used to redirect the returning sensor signal to the measuring optics and electronics. For both configurations, as with the other Mach-Zehnder configurations discussed above, one of the arms has a sensor window 1220.
While conventional Mach-Zehnder interferometer configurations are contemplated in the configurations noted above, more unconventional MZ configurations are also useful. As an example, unbalanced Mach-Zehnder interferometers or ring couplers may be used. Referring to FIGS. 21A, 21B, 21C, different configurations are illustrated that use unbalanced Mach-Zehnder interferometers. These configurations have a temperature independent output by using an appropriate combination of waveguides with different thermo-optic coefficients (dN_eff/dT). In FIG. 21A, an input signal enters input coupler 1400 and travels to a sensing window 1410 by way of a first waveguide 1420. The other arm 1430 from input coupler 1400 takes the signal to a second waveguide 1440 and from there by way of an output arm 1450 to output coupler 1460. Also entering output coupler 1460 is the first waveguide 1420 after passing by the sensor window 1410. The output coupler 1460 sends its output to a signal processing unit 1470. The first waveguide 1420, arm 1430, and output arm 1450 all have the thermo-optic coefficient of dn₁/dT while second waveguide 1440 has a thermo-optic coefficient dn₂/dT.
Referring to FIG. 21B, a different configuration of the unbalanced Mach-Zehnder interferometer is illustrated. The couplers 1400, 1460, the signal processing unit 1470, and sensor window 1410 are in the same places as well as the first waveguide 1420 and the other arm 1430 from the input coupler 1400. However, other arm 1430 now continues from the input coupler 1400 directly to output coupler 1460. The other waveguide 1440 travels from a junction point with first waveguide 1420 to the sensing window 1410 and then to another junction point adjacent the output coupler 1460. As with the above explanation, the first waveguide and the second waveguide have differing thermo-optic coefficients, with the first waveguide having a thermo-optic coefficient of dn₂/dT and the second waveguide having a thermo-optic coefficient of dn_i/dT.
In the configuration of FIG. 21C, three different waveguides are used. The first type of waveguide 1480 exits the input coupler 1400 while at the same time entering the output coupler 1460. The second type of waveguide 1490 couples the segments of the first waveguide between the two couplers 1400, 1460. The third waveguide 1495 couples the other segments of the first waveguide to one another with the sensing window in the middle of the third waveguide 1495. The second waveguide has length L1 and a thermo-optic coefficient of dn_i/dT while the third waveguide has length L2 and a thermo-optic coefficient of dn₂/dT.
In the configurations of FIGS. 21A-21C, the magnitude and sign of the effective thermo-optic coefficient of the silicon photonic wire waveguide can be controlled for example by selecting the waveguide core thickness, the cladding material, and the thickness of the cladding material. As examples, for glass, the dn/dT is approximately 1×10̂−5, for a typical polymer, the dn/dT is approximately on the order of −10⁻⁴, and for silicon dn/dT is approximately 2×10⁻⁴.
For the sensing window in a Mach-Zehnder interferometer, a photonic crystal structure, resonator, or grating may be used to increase the group index. This would thereby amplify the phase change induced by the molecular adsorption in the sensor window and increase sensitivity. (See FIG. 22)
It should be noted that the ring resonators and Mach-Zehnder based sensors may be used in different configurations possible with this sensor technology. An array of sensors (with each sensor being a ring resonator, Mach Zehnder, or other type of sensor) is also possible and such a configuration would allow for the use of a broadband light source as the input signal. Referring to FIG. 23, such a configuration is illustrated. A broadband light signal is used as the input and this is received by a wavelength demultiplexer or a 1×N splitter 1500. Each output of the demux/splitter 1500 passes through a specific sensor in a sensor array 1510. After passing through a sensor in the sensor array, each signal's characteristics are detected by a photodetector in a photodetector array 1520. The 1×N splitter may be a star coupler.
The configuration in FIG. 23 has photodetectors that are coplanar with the sensor array. However, this need not be the case. The signal may be coupled out of the surface of each output waveguide using mirrors or gratings or can be coupled out at the end facet of the array. Additionally, the input signal may be vertically coupled into the sensor array and then either vertically or horizontally coupled out. A configuration with vertical input and output coupling is illustrated in FIG. 24. In this configuration, an input beam array is coupled into the waveguides at input coupling points 1600. The waveguides 1610 guide the input signals into sensing windows 1620. Once each signal passes by a sensing window, it is then coupled out of the waveguide at output coupling point 1630. Multiple output coupling points 1630 may be available, with each output coupling point servicing at least one waveguide. Once the signal is coupled out of the waveguide, its characteristics can be detected by a phase detector array (PDA) 1640. It should be noted that coupling of signals from waveguide mode to vertical free space beam mode can be accomplished using etched 45 degree mirrors or diffraction grating structures.
If a single input signal and a single output signal is desired, a configuration as illustrated in FIG. 25 may be used. In FIG. 25, a single input optical signal 1700 with multiple wavelengths λ₁, λ₂, . . . λ_nis received by a wavelength multiplexer 1710. This multiplexer splits the incoming signal into different wavelengths and couples each signal with a specific one of a waveguide array 1720, with each one of the waveguide array 1720 having a sensor 1730 on the waveguide. After the signal has passed through one of the sensors 1730, it is then received by a wavelength demultiplexer 1740. If there are multiple signals received by the demultiplexer 1740, these signals are then combined into a single output signal 1750 with multiple wavelengths λ₁, λ₂, . . . λ_n.
A person understanding this invention may now conceive of alternative structures and embodiments or variations of the above all of which are intended to fall within the scope of the invention as defined in the claims that follow.

Claims

1. An optical sensor block for use in detecting molecules in a liquid or gas medium, the sensor block comprising:

a group of sensors comprising at least two sensor elements wherein each sensor element comprises

a substrate layer

a light waveguide sensor adjacent said medium

a lower cladding layer between said waveguide sensor and said substrate layer

wherein

molecular interactions at the waveguide sensor surface affect at least one characteristic of light travelling through said waveguide sensor

light travelling through said waveguide sensor is for eventual reception by an optical detector.

2. An optical sensor block according to claim 1 wherein said sensor block has a single optical input and said sensor block further comprises an optical signal splitting means.

3. An optical sensor block according to claim 1 wherein said sensor block has a plurality of optical inputs.

4. An optical sensor block according to claim 3, wherein said plurality of optical inputs are coupled to said sensors through an array of vertical waveguide couplers.

5. An optical sensor block according to claim 4, wherein at least one of said array of vertical waveguide couplers is a diffraction grating.

6. An optical sensor block according to claim 4 wherein at least one of said array of vertical waveguide couplers is a 45 degree mirror.

7. An optical sensor block according to claim 2 wherein said optical splitting means is an optical splitter for splitting said single optical input between said at least two sensor elements in said group.

8. An optical sensor block according to claim 2 wherein said optical splitting device is an optical demultiplexer for demultiplexing said single optical input between said at least two sensor elements in said group.

9. An optical sensor block according to claim 1 wherein at least one sensor element in said sensor block is configured as an optical ring resonator such that for said at least one sensor element, said light waveguide sensor is configured as a ring.

10. An optical sensor block according to claim 1 wherein at least one sensor element in said sensor block is configured as a two-mirror resonator, such that for said at least one sensor element, said light waveguide sensor is in a waveguide resonator cavity formed between two mirrors.

11. A sensor block according to claim 1 wherein at least one sensor element in said sensor block is configured as a spiral such that for said at least one sensor element, said light waveguide sensor adjacent said medium is arranged as a spiral.

12. A sensor block according to claim 1 wherein at least one sensor element in said sensor block has said light waveguide sensor arranged and configured as a single weft weaving pattern with each trace of said pattern being parallel to other traces to result in a grid-like pattern of parallel lines adjacent said medium

13. A sensor block according to claim 1 wherein at least one sensor element in said sensor block comprises waveguide sections with different dn/dT characteristics for reducing sensor temperature sensitivity.

14. A sensor block according to claim 9 wherein the or each of said at least one sensor element is configured as a ring resonator and has a specific resonance wavelength such that an input beam having said specific wavelength passes through said ring resonator.

15. An optical sensor block for use in detecting molecules in a liquid or gas medium, the sensor block comprising:

a Mach-Zehnder interferometer having a first and a second arm, said first arm being a sensor arm having an optical sensor element, said optical sensor element comprising:

a substrate layer

a light waveguide sensor adjacent said medium

a lower cladding layer between said waveguide sensor and said substrate layer

wherein

16. An optical sensor block according to claim 15 wherein said optical sensor element is configured as a ring resonator with said light waveguide sensor being configured as a ring.

17. An optical sensor block according to claim 15 wherein said second arm is a reference arm having a modulator.

18-21. (canceled)

22. A sensor for use in detecting molecules in a liquid or gas medium, the sensor comprising:

a substrate layer,

a light waveguide sensor element adjacent said medium

a lower cladding layer between said sensor element and said substrate layer

wherein

molecular interactions at the waveguide surface affect at least one characteristic of light travelling through said waveguide sensor element

and wherein said sensor element is configured as one arm of a Mach-Zehnder interferometer.

23. A sensor according to claim 22 wherein said sensor element comprises a thin, high refractive index contrast waveguide.

24. A sensor according to claim 22 wherein said sensor element comprises a silicon photonic waveguide.

25. A sensor according to claim 22 wherein said lower cladding layer comprises a layer of silicon oxide.