Patent Application
20060023220
Optical signals are detected in surface plasmon resonance (SPR) sensing and other optical measurement applications. In SPR sensing, intensity profiles associated with one or more received optical beams are established by detecting the intensities of optical beams as wavelengths of the optical beams are swept. The intensity profiles can then be used to detect and measure shifts in refractive indices that can indicate presence of biological analytes or biomolecular interactions within samples of an SPR sensor.
In some types of optical systems used in SPR sensing, resolution with which shifts in refractive indices can be measured increases with increases in the rate at which the intensities are detected. High measurement resolution is achieved in these systems when the rate at which the intensities are detected is high relative to the rate at which the wavelengths of the optical beams are swept.
Cameras that acquire images at video frame rates, for example sixty Hertz, can be used to detect the intensities of optical beams. However, when the wavelengths of the optical beams are swept at high speeds, the frame rate of the cameras is too low to achieve adequate measurement resolution for SPR sensing. Because image acquisitions involve processing detected signals from a large number of the optical sensors within the cameras, it is difficult to increase the rate of image acquisitions significantly beyond the video frame rate. Some types of cameras provide higher frame rates by reducing the number of optical sensors used to acquire images. These cameras typically restrict an image window to a single rectangular arrangement of optical sensors, thus limiting the ability of the camera to conform to the spatial arrangement of optical beams received by the camera. Accordingly, to achieve adequate measurement resolution in SPR sensing and other optical measurement applications, there is a need to detect the intensity of optical beams at a rate that is sufficiently higher than the frame rate of presently available cameras.
A multiplexed optical detector according to embodiments of the present invention includes a set of optical sensors coupled to a multiplexer. The multiplexer maps subsets of the optical sensors to at least one multiplexed output provided by the multiplexer. The subsets of optical sensors are configurable according to addresses that are provided to the multiplexer. Intensity profiles of optical beams illuminating the multiplexed optical detector can be detected by processing multiplexed signals present at the multiplexed outputs.
The set of optical sensors S in the multiplexed optical detector D is arranged in a one-dimensional array as shown in
The intensity profiles IP1-IPN established using the multiplexed optical detector D (shown in the exemplary plots of
The outputs 16 are electrodes, conductive pads, ball bonds, solder bumps, or other types of electrical contacts. Collectively, the sensor outputs 16 are arranged in a grid, array, or other configuration that provides a suitable interface for an input section 18 of the multiplexer 10 that has multiple input contacts. In one embodiment, groups of the input contacts are hard-wired together in the input section 18 to define clusters Cx of optical sensors. In the example where the multiplexed optical detector D includes sixteen thousand optical sensors, hard-wired groups of input contacts define clusters Cx of four optical sensors 12 to provide an appropriate trade-off between spatial resolution of the multiplexed optical detector D and complexity of the circuitry of the multiplexer 10. However, alternative embodiments of the present invention include hard-wired groups of input contacts that define clusters of one or more optical sensors 12.
The input section 18 of the multiplexer 10 couples the clusters of optical sensors S to multiple amplifiers A in a parallel configuration. Typically, the amplifiers A are transimpedance amplifiers that convert currents Ix or other detected signals provided by the clusters Cx of optical sensors 12 to a corresponding detected signal, such as a voltage Vx. The subscript “x” of the element reference designators is an integer variable that is used to refer to any particular one of the clusters Cx of optical sensors 12 in the set of optical sensors S, the current Ix provided by the cluster Cx, and any particular one of the amplifiers Ax and the voltage Vx provided by the particular amplifier Ax. Accordingly, the cluster Cx represents any of the clusters of optical sensors 12, and the amplifier Ax represents the one of the amplifiers A that is coupled to the cluster Cx. In the example where the multiplexed optical detector D includes sixteen thousand optical sensors and where the clusters Cx include four optical sensors 12, the multiplexer includes four thousand amplifiers A. The voltage Vx provided by each amplifier Ax is the detected signal that represents the intensity of the optical beam B illuminating the cluster Cx of the optical sensors 12.
In the example where the multiplexed optical detector D includes four thousand amplifiers A, the multiplexer 10 includes four thousand sample-and-hold circuits SH. The sample-and-hold circuits SH are strobed by a timing signal 13, typically provided by a clock 20 or other suitable timing source. The sample-and-hold circuits SH are coupled to corresponding analog hold circuits AH in a parallel configuration. In the example where there are four thousand sample-and-hold circuits SH, the multiplexer 10 includes four thousand analog hold circuits AH. The analog hold circuits AH are strobed by the timing signal 13, as delayed by a delay element 22 to form a delayed timing signal 17.
The analog hold circuits AH are coupled to the inputs to a bank of programmable switches 24. In one embodiment, the bank of programmable switches 24 includes a first series of analog multiplexers M1 in a parallel arrangement. Each analog multiplexer M1 in the first series provides eight-to-one multiplexing. The bank of programmable switches 24 also includes a second series of analog multiplexers M2 in a parallel arrangement. Each analog multiplexer M2 in the second series provides eight-to-one multiplexing. The bank of programmable switches 24 also includes a third series of analog multiplexers M3 in a parallel arrangement. Each analog multiplexer M3 in the third series provides eight-to-one multiplexing. In the example wherein the multiplexer 10 includes four thousand sample-and-hold circuits SH, the first series of analog multiplexers M1 includes five hundred analog multiplexers M1, the second series of analog multiplexers M2 includes sixty-three analog multiplexers M2 and the third series of analog multiplexers M3 includes one analog multiplexer M3. In the multiplexer 10 shown in
The bank of programmable switches 24 provides mappings between clusters Cx of optical sensors 12 at designated physical locations in the set of optical sensors S and the multiplexed output 26, that can be configured according to selectable addresses 15 provided to the bank of programmable switches 24 by a processor 28. In the embodiment of the present invention wherein the bank of programmable switches 24 includes the first series of analog multiplexers M1, the second series of analog multiplexers M2, and the third series of analog multiplexers M3, each address 15 provided by the processor 28 includes an address 15a to select an input of one analog multiplexer M1 in the first series of analog multiplexers M1, an address 15b to select the input of the analog multiplexer M2 in the second series of analog multiplexers M2 that is coupled to the output of the analog multiplexer M1 addressed in the first series, and an address 15c of the input of the analog multiplexer M3 in the third series of analog multiplexers M3 that is coupled to the output of the analog multiplexer M2 addressed in the second series.
The mapping provided by the bank of programmable switches 24 is a selective coupling of designated ones of the analog hold circuits AH to the multiplexed output 26, designated according to the addresses 15 that are provided by the processor 28 to the bank of programmable switches 24. For example, providing the address to the bank of programmable switches 24 that corresponds to the cluster Cx directs the voltage Vx stored in the analog hold circuit AHx to the multiplexed output 26 of the multiplexer 10. Selecting the address to the bank of programmable switches 24 that corresponds to the cluster Cy (not shown) directs a voltage Vy (not shown) stored in the analog hold circuit AHy (not shown) to the multiplexed output 26 of the multiplexer 10, and so on.
The multiplexed output 26 is typically coupled to a data acquisition system, signal digitizer, or other type of analog-to-digital converter ADC. In the embodiment of the present invention shown in
The multiplexed optical detector D is suitable for detecting the intensity of optical beams B in a variety of optical systems. Detecting optical intensity typically includes shifting a detected signal provided by the optical sensors 12, such as the voltages from the sample-and-hold circuits SH, into the analog hold circuits AH, and then selectively coupling designated ones of the analog hold circuits AH to the multiplexed output 26 according to the addresses 15 provided by the processor 28. The voltages provided at the multiplexed output 26 over time form the multiplexed signal 19. In typical applications of the multiplexed optical detector D, the multiplexed signal 19 is digitized and further processed.
Operation of the multiplexed optical detector D can be tailored to the optical system in which the multiplexed optical detector D is used. For the purpose of illustration, the operation of the multiplexed optical detector D is described in the context of SPR sensing. In SPR sensing, wavelengths of one or more optical beams illuminating an SPR sensor 10 are swept over a designated wavelength range in a designated time interval. For example, the wavelength of an optical beam B can be swept over a wavelength range from 1500 nm to 1600 nm in a time interval of 1.5 seconds. Intensity of the optical beam B illuminating the optical sensors is detected by the multiplexed optical detector D as the wavelength of the optical beam B is swept. To achieve a measurement resolution of 100 picometers in this example, one thousand measurements that are equi-spaced in wavelength are acquired over the 100 nm wavelength range.
In a typical measurement acquisition, the timing signal 13 strobes the sample-and- hold circuits SH at time intervals of 1.5 ms, as defined by the cycles of the timing signal 13. The delayed timing signal 17 strobes the analog hold circuits AH, also at time intervals of 1.5 ms, defined by the cycles of the delayed timing signal 17. According to each strobe, or cycle, of the timing signal 13 the switches in the sample-and-hold circuits SH are closed to charge the capacitors within the sample-and-hold circuits SH, while switches in the analog hold circuits AH are open. Once the capacitors within the sample-and-hold circuits SH are charged, the switches within the sample-and-hold circuits SH are opened and switches within the analog hold circuits AH are closed by the delayed timing signal 17 to charge the capacitors within the analog hold circuits AH. Once the capacitors within the analog hold circuits AH are charged, the switches within the analog hold circuits AH are opened to isolate the sample-and-hold circuits SH from the analog hold circuits AH. This switching sequence provides isolation between the sample-and-hold circuits SH and the bank of programmable switches 24, and provides for the shifting of voltages on the sample-and-hold circuits SH to the analog hold circuits AH. The switching sequence is repeated within each cycle of the timing signal 13, which in this example is each 1.5 ms.
Within each cycle of the timing signal, or each 1.5 ms time interval in this example, the processor 28 provides a predetermined set of addresses 15, sequentially, to the bank of programmable switches 24. According to the set of addresses 15, designated ones of the analog hold circuits AH are sequentially coupled to the multiplexed output 26. This enables the voltages on the designated analog hold circuits AH to be selectively provided at the multiplexed output 26. Different ones of the analog hold circuits AH selectively coupled to the multiplexed output 26 can be designated by changing the addresses included in the predetermined set of addresses 15.
A multiplexed signal 19 provided at the multiplexed output 26 is shown in the exemplary plot of
In SPR sensing, the clusters Cx of optical sensors 12 that are selectively coupled to the multiplexed output 26 according to the predetermined set of addresses 15 typically comprise a small percentage of the total number of optical sensors S in the multiplexed optical detector D. This enables the intensities of optical beams intercepted by the multiplexed optical detector D to be detected at a high rate, for example by increasing the frequency of the clock 20. In addition, since the selective coupling of the clusters C1, C2, Cx of optical sensors S are selectively coupled to the multiplexed output 26 according to the addresses 15 provided to the bank of programmable switches 24 in the multiplexer 10, the subsets S1-SN of optical sensors 12 can be arbitrarily sequenced or arranged within the set of optical sensors S. Thus, because the subsets S1-SN of optical sensors 12 are individually addressable according to the addresses provided by the processor 28, the subsets S1-SN can form any spatial arrangement, including spatial arrangements that conform to the optical beams received by the set of optical sensors S, and spatial arrangements wherein the subsets SI1-SN are not contiguous.
The multiplexed signal 19 can be further processed by systems or components coupled to the multiplexed output 26, depending on the type of optical system within which the multiplexed optical detector D is included. In one example, the multiplexed signal 19 is digitized and then demultiplexed to provide a demultiplexed signal 21 as shown in the exemplary plot of
In SPR sensing, multiple clusters of optical sensors 12 are typically formed into the subsets S1-SN of optical sensors S that are associated with the samples T1-TN of the SPR sensor 2, as shown in
The predetermined set of addresses 15 that are provided to the bank of programmable switches 24 are established in various ways. In one example, the set of addresses 15 is established according to a preselection method 40 shown in the flow diagram of
The subsets S1-SN are then defined (step 48) based on the voltage values that result from the illumination by the optical beam B. In one example, the subsets S1-SN of the set of optical sensors S are defined by displaying the contents of the memory 30 on a computer display or other output device (not shown), and then selecting memory locations corresponding to the clusters of optical sensors 12 through a user interface (not shown) based on brightness or other characteristics observed on the output device. Software tools, such as LabView Vision Assistant, available from National Instruments Corp. in Austin, Tex., USA, are suitable for displaying the contents of the memory 30 and for selecting clusters of optical sensors 12 at designated physical locations within the set of optical sensors S.
In another example, the subsets S1-SN of optical sensors S are selected automatically based on the magnitude of the voltage values stored in the memory 30. If the wavelength of the optical beam B applied to the SPR sensor 2 is set close to the resonant wavelength R1-RN of the samples T1-TN (shown in
Additional or alternative criteria can be used to establish the set of addresses 15 used to define the subsets S1-SN of optical sensors 12. For example, the set of addresses 15 defining the subsets S1-SN of optical sensors 12 can be selected to exclude optical sensors 12 that have dark currents outside of a specified range, excessive leakage from other optical sensors 12, shorted outputs 16, or other defects in the set of optical sensors S or the multiplexer 10. The set of addresses 15 can also be selected to exclude undesired characteristics that result from the optical path traversed by the optical beams received by the set of optical sensors S.
The block diagram shown in
While the embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to these embodiments may occur to one skilled in the art without departing from the scope of the present invention as set forth in the following claims.
