WO2014035389A1 - System and method of providing wideband wavelength optical detection using sandwich detector - Google Patents

System and method of providing wideband wavelength optical detection using sandwich detector Download PDF

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Publication number
WO2014035389A1
WO2014035389A1 PCT/US2012/052905 US2012052905W WO2014035389A1 WO 2014035389 A1 WO2014035389 A1 WO 2014035389A1 US 2012052905 W US2012052905 W US 2012052905W WO 2014035389 A1 WO2014035389 A1 WO 2014035389A1
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WO
WIPO (PCT)
Prior art keywords
optical detector
detector
amplifier
generate
wavelength
Prior art date
Application number
PCT/US2012/052905
Other languages
French (fr)
Inventor
Zhuoyun Li
Dae Han
Kathy ZADROVICZ
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Newport Corporation
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Application filed by Newport Corporation filed Critical Newport Corporation
Priority to PCT/US2012/052905 priority Critical patent/WO2014035389A1/en
Publication of WO2014035389A1 publication Critical patent/WO2014035389A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/4228—Photometry, e.g. photographic exposure meter using electric radiation detectors arrangements with two or more detectors, e.g. for sensitivity compensation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/2803—Investigating the spectrum using photoelectric array detector
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/30—Measuring the intensity of spectral lines directly on the spectrum itself
    • G01J3/32—Investigating bands of a spectrum in sequence by a single detector
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
    • G01J3/50—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors
    • G01J3/51—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters
    • G01J3/513—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters having fixed filter-detector pairs
    • G01J2003/516—Measurement of colour; Colour measuring devices, e.g. colorimeters using electric radiation detectors using colour filters having fixed filter-detector pairs with several stacked filters or stacked filter-detector pairs

Definitions

  • This disclosure relates generally to photo or optical detection, and in particular, to a system and method of providing wideband wavelength optical detection using a sandwich detector.
  • Optical detectors or photodiodes are manufactured from a number of distinct materials, each material offering sensitivity within a distinct range of the electromagnetic spectrum.
  • silicon-based detectors typically produce significant photocurrents (e.g., > 0.005 Amp/Watt) when irradiated with radiation having a wavelength from about 200 nanometers (nm) to about llOOnm.
  • germanium-based detectors produce significant photocurrents when irradiated with radiation having a wavelength from about 700nm to about 1800nm.
  • indium-gallium-arsenide-based detectors are commonly used to detect optical signals having a wavelength from about 800nm to about 2600nm, while lead sulfide-based photodiodes are used to detect optical signals having a wavelength of about lOOOnm to about 3500nm.
  • optical detectors or photodiodes of different types are typically swapped when measuring signals having distinct and far-apart wavelengths.
  • a silicon-based detector may be used to perform detection of an optical signal having a wavelength of 800nm, and then the silicon-based detector is swapped for a germanium-based detector to perform detection of another optical signal having a wavelength of 1500nm.
  • the swapping of detectors is often cumbersome, time-consuming, and generally undesirable.
  • pyro electric detectors generally provide a greater range of wavelength detection without requiring distinct devices and a selection switch.
  • pyro electric detectors generate a current in response to temperature change in a crystal material due to incident radiation. The temperature change is generally insensitive to the wavelength of the incident radiation, thus providing a wide range of wavelength detection.
  • such detectors generally have high noise level, and thus, are generally incapable of producing detection signals with a desirable signal to noise ratio (SNR).
  • SNR signal to noise ratio
  • An aspect of the disclosure relates to an optical detector that is capable of wideband wavelength detection of incident radiation with relatively good noise performance and without the need of a switch to select different types of optical detecting elements.
  • the optical detector comprises a sandwich detector including a window, a first detecting element (e.g., a first photodiode), and a second detecting element (e.g., a second photodiode).
  • the first detecting element is configured to generate a first photocurrent in response to first incident radiation with a wavelength within a first wavelength range.
  • the first detecting element is configured to receive the first incident radiation by way of the window.
  • the second detecting element is configured to generate a second photocurrent in response to second incident radiation with a wavelength in a second wavelength range.
  • the second wavelength range is different than the first wavelength range, although the ranges may overlap.
  • the second detecting element is configured to receive the second incident radiation by way of the window and the first detecting element.
  • the optical detector further comprises a first amplifier, such as a transimpedance amplifier, configured to generate to generate a first signal, such as a first voltage, based on the first photocurrent generated by the first detecting element of the sandwich detector.
  • the optical detector further comprises a second amplifier, such as a transimpedance amplifier, configured to generate to generate a second signal, such as a second voltage, based on the second photocurrent generated by the second detecting element of the sandwich detector.
  • the gains, such as the transimpedance gains, of the first and second amplifiers may be user adjustable or selectable.
  • the summing device may comprise a first inverting amplifier configured to receive the first and second signals or voltages from the amplifiers by way of respective resistors.
  • a second inverting amplifier may be provided following the first inverting amplifier to change the polarity of the voltage at the output of the first inverting amplifier in order to generate the detector's output voltage.
  • the first and second detecting elements may comprise any number of distinct photodiodes, such as a silicon-based photodiode, a germanium-based photodiode, an indium-gallium-arsenide-based photodiode, and a lead-sulfide- based photodiode, just to name a few.
  • the first and second detecting elements may be of the same type of material, but configured for detecting incident radiation in distinct wavelength bands. Or, the first and second detecting element may be of different materials, also configured for detecting incident radiation in distinct wavelength bands. It shall be understood that the sandwich detector may comprise more than two detecting elements.
  • FIG. 1 illustrates a block diagram of an exemplary wideband wavelength optical detector in accordance with an aspect of the disclosure.
  • FIG. 2 illustrates a block diagram of another exemplary wideband wavelength optical detector in accordance with another aspect of the disclosure.
  • FIG. 3 illustrates a flow diagram of an exemplary method of calibrating the exemplary wideband optical detector in accordance with another aspect of the disclosure.
  • FIG. 4 illustrates a graph of an exemplary responsivity response of the exemplary wideband optical detector in accordance with another aspect of the disclosure.
  • FIG. 1 illustrates a block diagram of an exemplary wideband wavelength optical detector 100 in accordance with an aspect of the disclosure.
  • the optical detector 100 includes a sandwich detector including a plurality of distinct detectors (e.g., photodiodes) configured to generate significant photocurrents based on incident radiation within distinct wavelength bands, respectively.
  • the optical detector 100 also includes a plurality of transimpedance amplifiers to convert the photocurrents into voltages.
  • the optical detector 100 includes a summing device configured to sum the voltages together to generate an output voltage. By proper selection of the distinct detectors of the sandwich detector, the optical detector 100 may be configured for wideband wavelength detection of incident radiation.
  • the optical detector 100 comprises a sandwich detector 110, a first amplifier 120-1, a second amplifier 120-2, and a summing device 130.
  • the sandwich detector 110 comprises a first detector 112-1 and a second detector 112-2, both of which may be configured as photodiodes.
  • the sandwich detector 110 is configured to receive radiation, which could be of distinct wavelengths, by way of a window or opening 114.
  • the window 114, first detector 112-1, and second detector 112-2 are oriented in a substantially vertically stacked manner.
  • the first detector 112-1 of the sandwich detector 110 is configured to generate a significant photocurrent Ii in response to incident radiation having a wavelength ⁇ in the range of ⁇ ⁇ ⁇ .
  • the first detector 112-1 is configured to receive the incident radiation by way of the window 114 of the sandwich detector 110.
  • the first detector 110 may be configured to generate a significant photocurrent Ii with responsivity greater than a defined threshold (e.g., 0.005 Amp/Watt) for incident radiation having a wavelength ⁇ in the range of ⁇ ⁇ ⁇ .
  • a defined threshold e.g., 0.005 Amp/Watt
  • the first detector 112-1 may be a silicon-based photodiode configured to generate a significant photocurrent Ii for incident radiation having a wavelength from about 200nm to about llOOnm.
  • the second detector 112-2 of the sandwich detector 110 is configured to generate a significant photocurrent I2 in response to incident radiation having a wavelength ⁇ 2 in the range of ⁇ ⁇ 2.
  • the second detector 112-2 is configured to receive this radiation by way of the window 114 and the first detector 112-1.
  • the second detector 112-2 is configured to generate a significant photocurrent I2 with responsivity greater than a defined threshold (e.g., 0.005 Amp/Watt) for incident radiation having a wavelength ⁇ 2 in the range of ⁇ ⁇ 2.
  • a defined threshold e.g., 0.005 Amp/Watt
  • the second detector 112-2 may be a germanium-based photodiode configured to generate a significant photocurrent I2 for incident radiation having a wavelength from about 700nm to about 1800nm.
  • the first amplifier 120-1 may be configured as a transimpedance amplifier. That is, the first amplifier 120-1 may be configured to receive the first photocurrent Ii generated by the first detector 112-1 in response to incident radiation with a wavelength ⁇ within the range of ⁇ ⁇ ⁇ , and generate a corresponding voltage Vi from the photocurrent Ii based on a defined transimpedance gain.
  • the second amplifier 120-2 may also be configured as a transimpedance amplifier. That is, the second amplifier 120-2 may be configured to receive the second photocurrent I2 generated by the second detector 112-2 in response to incident radiation with a wavelength ⁇ 2 within the range of ⁇ ⁇ 2, and generate a corresponding voltage V2 from the photocurrent I2 based on a defined transimpedance gain.
  • the summing device 130 is configured to combine or sum the voltages Vi and V2 together to generate an output voltage V ou t for the optical detector 100.
  • the sandwich detector 110 has distinct detectors 112-1 and 112-2 capable of generating significant photocurrents in response to incident radiation of distinct wavelength bands, the output voltage V ou t is consequently responsive to wideband incident radiation.
  • the optical detector 100 has the advantage of providing wideband detection without the use of a switching device to select the appropriate detector, as commonly employed in prior art wideband detectors.
  • the sandwich detector 110 uses photodiodes, it is not prone to significant noise, as is a pyro electric detector.
  • the sandwich detector 110 comprises two distinct detectors 112-1 and 112-2, it shall be understood that the sandwich detector 110 may comprise more than two detectors.
  • another embodiment may comprise three distinct detectors configured in a substantially vertically stacked orientation.
  • such sandwich detector may comprise three distinct photodiodes based on silicon, germanium, and indium- gallium-arsenide, so that the optical detector is able to detect incident radiation having a wavelength between about 200nm and about 2600nm.
  • Another embodiment may comprise four distinct detectors configured in a substantially vertically stacked orientation.
  • such sandwich detector may comprise four distinct photodiodes based on silicon, germanium, indium-gallium- arsenide, and lead- sulfide, so that the optical detector is able to detect incident radiation having a wavelength between about 200nm and about 3500nm.
  • Various combinations of distinct detectors may be implemented in a sandwich detector in order to provide the optical detector with a specified wavelength band detection capability. Further, as exemplified, it shall be understood that the wavelength detection ranges of the distinct detectors in a sandwich detector may overlap. In the overlap region, the optical detector has a responsivity that is substantially the sum of the responsivity of the individual detectors in that region. Thus, in the overlap region, the optical detector provides increased responsivity for better detection of low power signals.
  • FIG. 2 illustrates a block diagram of another exemplary wideband wavelength optical detector 200 in accordance with another aspect of the disclosure.
  • the optical detector 200 may be an exemplary more detailed implementation of the optical detector 100, previously discussed.
  • the optical detector 200 comprises a sandwich detector including distinct detectors (e.g., photodiodes) configured to detect incident radiation in distinct wavelength bands, respectively.
  • the optical detector further comprises user- configurable gain amplifiers configured to amplify the photocurrents generated by the distinct detectors of the sandwich detector, respectively.
  • the optical detector 200 comprises a pair of cascaded inverting amplifiers configured to sum the voltages generated at the outputs of the amplifiers, and produce an output voltage for the optical detector 200.
  • the optical detector 200 comprises a sandwich detector 210, a first amplifier 220-1 and corresponding circuitry, such as gain select 222-1 and resistors R11-R14, for providing gain adjustment of the first amplifier by a user, and a second amplifier 220-2 and corresponding circuitry, such as gain select 222-2 and resistors R21-R24, for providing gain adjustment of the second amplifier by a user.
  • the optical detector 200 comprises a first inverting amplifier 230 and gain setting and summing circuitry, such as resistors R32, R34, and R36.
  • the optical detector 200 comprises a second inverting amplifier 240 and gain setting circuitry, such as R42 and R44.
  • the sandwich detector 210 comprises a first detector 212-1, a second detector 212-2, and a window 214, all of which are configured substantially in a vertically stacked orientation.
  • the first detector 212-1 is configured to generate a significant photocurrent Ii (e.g., with a responsivity > 0.005 Amp/Watt) in response to incident radiation with a wavelength ⁇ in a range of ⁇ ⁇ ⁇ .
  • the first detector 212-1 is configured to receive incident radiation ⁇ by way of the window 214.
  • the second detector 212-2 is configured to generate a significant photocurrent I2 (e.g., with a responsivity > 0.005 Amp/Watt) in response to incident radiation with a wavelength ⁇ 2 in a range of ⁇ ⁇ 2.
  • the second detector 212-2 is configured to receive the incident radiation ⁇ 2 by way of the window 214 and the first detector 212-1.
  • the sandwich detector 210 may comprise more than two distinct detectors.
  • the first and second detectors 212-1 and 212-2 have a grounded terminal coupled together and to positive input terminals of the first and second amplifiers 220-1 and 220-2.
  • the terminal of the first detector 212-1 at which the photocurrent Ii is generated is coupled to a negative input terminal of the first amplifier 220-1.
  • the terminal of the second detector 212-2 at which the photocurrent I2 is generated is coupled to a negative input terminal of the second amplifier 220-2.
  • the first and second amplifiers 220-1 and 220-2 may be configured as transimpedance amplifiers to generate voltages Vi and V2 by applying transimpedance gains on the first and second photocurrents Ii and I2, respectively.
  • the optical detector 200 includes circuitry to allow a user to set the transimpedance gains of the first and second amplifiers 220-1 and 220-2.
  • the optical detector 200 comprises a first bank of resistors R11-R14 and a first gain select circuit 222-1, both coupled in series between the output and the negative input of the first amplifier 220-1 in a feedback configuration.
  • the first gain select circuit 222-1 operates as a multiplexer configured to couple one or more of the resistors Rll- R14 to the negative input of the first amplifier 220-1 based on a user input.
  • the transimpedance gain of the first amplifier 220-1 is based on which one or more of the resistors R11-R14 are coupled to the negative input and output of the first amplifier.
  • the resistors R11-R14 may be configured as a binary (e.g., 10kQ, 20kQ, 40kQ, and 80kQ), decimal (e.g., 10kQ, 100kQ, 1 ⁇ , and 10 ⁇ ), or other type of resistor bank.
  • the optical detector 200 comprises a second bank of resistors R21-R24 and a second gain select circuit 222-2, both coupled in series between the output and the negative input of the second amplifier 220-2 in a feedback configuration.
  • the second gain select circuit 222-2 operates as a multiplexer configured to couple one or more of the resistors R21-R24 to the negative input of the second amplifier 220-2 based on a user input.
  • the transimpedance gain of the second amplifier 220-2 is based on which one or more of the resistors R21-R24 is coupled to the negative input and output of the second amplifier.
  • the resistors R21-R24 may be configured as a binary (e.g., 10kQ, 20kQ, 40kQ, and 80kQ), decimal (e.g., 10kQ, 100kQ, 1 ⁇ , and 10 ⁇ ), or other type of resistor bank.
  • the first inverting amplifier 230 applies respective gains to the voltages Vi and V2 based on the ratio of resistor R36 over R32 and the ratio of resistor R36 over R34, respectively. More specifically, the voltage at the output of the first inverting amplifier 230 may be equal to - (R36/R32 * Vi + R36/R34 * V2).
  • the second inverting amplifier 240 applies a gain to the voltage at the output of the first inverting amplifier 230 based on a ratio of resistor R44 over R42 to generate an output voltage V ou t for the optical detector 200. More specifically, the output voltage Vout may be equal to R44/R42 * (R36/R32 * Vi + R36/R34 * V 2 ).
  • the wavelength detection ranges of the distinct detectors in a sandwich detector may overlap.
  • the optical detector has a responsivity that is substantially the sum of the responsivity of the individual detectors in that region.
  • the optical detector provides increased responsivity for better detection of low power signals.
  • FIG. 3 illustrates a flow diagram of an exemplary method 300 of calibrating the exemplary wideband optical detector in accordance with another aspect of the disclosure.
  • the method 300 is configured to generate a table of responsivity for different input wavelengths optical signals.
  • a user may be able to determine the input power of the signal applied to the detector using the table.
  • the table may be stored internally in the detector through the use of a non-volatile memory, or the table may be stored in a compact disk or the like, which is provided to the user upon acquiring the optical detector.
  • a variable i is set to zero (0), which keep tracks of the current input wavelength signal from which the responsivity of the detector is being measured (block 302). Then, according to the method 300, an optical signal with a wavelength Xi is applied to the input of the wideband optical detector (block 304). The power of the input optical signal is measured with a calibrated device (block 306).
  • a measurement of the photocurrent current or voltage at the output of the detector is taken (block 308).
  • the photocurrent may be measured directly.
  • the photocurrent is substantially Ii.
  • the photocurrent is substantially I2.
  • the photocurrent is substantially Ii + I2.
  • the applicable photocurrent may also be measured indirectly by measuring the output voltage Vout, since the output voltage V ou t is a function of the applicable photocurrents and the aggregate gain applied to the photocurrents.
  • the optical detector may include an internal memory, such as a non-volatile memory, in which the table may be stored.
  • the responsivity table may be recorded on a compact disk or other portable memory, and provided to a user upon acquiring the optical detector.
  • FIG. 4 illustrates a graph of an exemplary responsivity response of an exemplary wideband optical detector in accordance with another aspect of the disclosure.
  • a wideband optical detector that employs a sandwich detector comprising a first detector being a silicon-based photodiode and a second detector being a germanium-based photodiode.
  • a silicon-based detector is capable of detecting or generating significant photocurrent (e.g., with a responsivity > 0.005 Amp/Watt) in response to incident radiation with a wavelength in the range of 200nm to about llOOnm.
  • a germanium-based detector is capable of detecting or generating significant photocurrent in response to incident radiation with a wavelength in the range of 700nm to about 1800nm.
  • an optical detector that employs a sandwich detector with a first detector being a silicon-based detector and a second detector being a germanium-based detector in accordance with the teachings herein will have a significant responsivity (e.g., responsivity > 0.005 Amp/Watt) for wavelengths extending from 200nm to 1800nm.
  • responsivity e.g., responsivity > 0.005 Amp/Watt
  • the optical detector in accordance with the teachings herein, serves as a useful measurement equipment for wideband optical detection applications and usability.

Abstract

The disclosure relates to an optical detector that is capable of wideband wavelength detection of incident radiation with relatively good noise performance and without the need of a switch to select different types of optical detecting elements. The optical detector includes a sandwich detector with distinct photo or optical detecting elements configured to generate photocurrents in response to incident radiation of distinct wavelength ranges, respectively. The optical detector further includes transimpedance amplifiers configured to generate voltages based on the photocurrents, respectively. Additionally, the optical detector includes a summing device configured to generate an output voltage by summing the voltages from the amplifiers. The optical detector effectively operates as a single detector but with a detection range based on the combined wavelength bands of the distinct detecting elements of the sandwich detector. The distinct wavelength bands may overlap, and in the overlap region, the optical detector exhibits greater responsivity.

Description

SYSTEM AND METHOD OF PROVIDING WIDEBAND WAVELENGTH OPTICAL DETECTION USING SANDWICH DETECTOR
FIELD
[ 0001 ] This disclosure relates generally to photo or optical detection, and in particular, to a system and method of providing wideband wavelength optical detection using a sandwich detector.
BACKGROUND
[ 0002 ] Optical detectors or photodiodes are manufactured from a number of distinct materials, each material offering sensitivity within a distinct range of the electromagnetic spectrum. For example, silicon-based detectors typically produce significant photocurrents (e.g., > 0.005 Amp/Watt) when irradiated with radiation having a wavelength from about 200 nanometers (nm) to about llOOnm. In contrast, germanium-based detectors produce significant photocurrents when irradiated with radiation having a wavelength from about 700nm to about 1800nm. Similarly, indium-gallium-arsenide-based detectors are commonly used to detect optical signals having a wavelength from about 800nm to about 2600nm, while lead sulfide-based photodiodes are used to detect optical signals having a wavelength of about lOOOnm to about 3500nm.
[ 0003 ] Because of their wavelength selectivity, optical detectors or photodiodes of different types are typically swapped when measuring signals having distinct and far-apart wavelengths. For instance, during a measurement, a silicon-based detector may be used to perform detection of an optical signal having a wavelength of 800nm, and then the silicon-based detector is swapped for a germanium-based detector to perform detection of another optical signal having a wavelength of 1500nm. For users performing such measurements of distinct wavelength signals, the swapping of detectors is often cumbersome, time-consuming, and generally undesirable.
[ 0004 ] To address these issues, manufacturers of optical detectors have incorporated different types of optical detectors into a single unit with a switch for selecting the appropriate detector. Thus, taking the above example, a user operates the switch to select the silicon-based detector to measure the optical signal having a wavelength of 800nm, and then operates the switch to select the germanium-based detector to measure the optical signal having a wavelength of 1500nm. Although such multi- detector devices improve the process of measuring distinct wavelengths signals, these devices still require users to specifically select the appropriate detector type.
[ 0005 ] Other types of optical detectors, such as pyro electric detectors, generally provide a greater range of wavelength detection without requiring distinct devices and a selection switch. For instance, pyro electric detectors generate a current in response to temperature change in a crystal material due to incident radiation. The temperature change is generally insensitive to the wavelength of the incident radiation, thus providing a wide range of wavelength detection. However, such detectors generally have high noise level, and thus, are generally incapable of producing detection signals with a desirable signal to noise ratio (SNR).
[ 0006 ] Thus, there is an ongoing need for an optical detector capable of detecting an incident signal with high responsivity over a wide range of wavelengths with substantially improved SNR performance.
SUMMARY
[ 0007 ] An aspect of the disclosure relates to an optical detector that is capable of wideband wavelength detection of incident radiation with relatively good noise performance and without the need of a switch to select different types of optical detecting elements.
[ 0008 ] In particular, the optical detector comprises a sandwich detector including a window, a first detecting element (e.g., a first photodiode), and a second detecting element (e.g., a second photodiode). The first detecting element is configured to generate a first photocurrent in response to first incident radiation with a wavelength within a first wavelength range. The first detecting element is configured to receive the first incident radiation by way of the window. The second detecting element is configured to generate a second photocurrent in response to second incident radiation with a wavelength in a second wavelength range. The second wavelength range is different than the first wavelength range, although the ranges may overlap. The second detecting element is configured to receive the second incident radiation by way of the window and the first detecting element.
[ 0009 ] The optical detector further comprises a first amplifier, such as a transimpedance amplifier, configured to generate to generate a first signal, such as a first voltage, based on the first photocurrent generated by the first detecting element of the sandwich detector. Similarly, the optical detector further comprises a second amplifier, such as a transimpedance amplifier, configured to generate to generate a second signal, such as a second voltage, based on the second photocurrent generated by the second detecting element of the sandwich detector. The gains, such as the transimpedance gains, of the first and second amplifiers may be user adjustable or selectable.
[ 0010 ] The summing device may comprise a first inverting amplifier configured to receive the first and second signals or voltages from the amplifiers by way of respective resistors. A second inverting amplifier may be provided following the first inverting amplifier to change the polarity of the voltage at the output of the first inverting amplifier in order to generate the detector's output voltage.
[ 0011 ] The first and second detecting elements may comprise any number of distinct photodiodes, such as a silicon-based photodiode, a germanium-based photodiode, an indium-gallium-arsenide-based photodiode, and a lead-sulfide- based photodiode, just to name a few. The first and second detecting elements may be of the same type of material, but configured for detecting incident radiation in distinct wavelength bands. Or, the first and second detecting element may be of different materials, also configured for detecting incident radiation in distinct wavelength bands. It shall be understood that the sandwich detector may comprise more than two detecting elements. [ 0012 ] Other aspects, advantages and novel features of the disclosure will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[ 0013 ] FIG. 1 illustrates a block diagram of an exemplary wideband wavelength optical detector in accordance with an aspect of the disclosure.
[ 0014 ] FIG. 2 illustrates a block diagram of another exemplary wideband wavelength optical detector in accordance with another aspect of the disclosure.
[ 0015 ] FIG. 3 illustrates a flow diagram of an exemplary method of calibrating the exemplary wideband optical detector in accordance with another aspect of the disclosure.
[ 0016 ] FIG. 4 illustrates a graph of an exemplary responsivity response of the exemplary wideband optical detector in accordance with another aspect of the disclosure.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[ 0017 ] FIG. 1 illustrates a block diagram of an exemplary wideband wavelength optical detector 100 in accordance with an aspect of the disclosure. As discussed in more detail herein, the optical detector 100 includes a sandwich detector including a plurality of distinct detectors (e.g., photodiodes) configured to generate significant photocurrents based on incident radiation within distinct wavelength bands, respectively. The optical detector 100 also includes a plurality of transimpedance amplifiers to convert the photocurrents into voltages. Additionally, the optical detector 100 includes a summing device configured to sum the voltages together to generate an output voltage. By proper selection of the distinct detectors of the sandwich detector, the optical detector 100 may be configured for wideband wavelength detection of incident radiation. [ 0018 ] In particular, the optical detector 100 comprises a sandwich detector 110, a first amplifier 120-1, a second amplifier 120-2, and a summing device 130. The sandwich detector 110, in turn, comprises a first detector 112-1 and a second detector 112-2, both of which may be configured as photodiodes. As shown, the sandwich detector 110 is configured to receive radiation, which could be of distinct wavelengths, by way of a window or opening 114. The window 114, first detector 112-1, and second detector 112-2 are oriented in a substantially vertically stacked manner.
[ 0019 ] The first detector 112-1 of the sandwich detector 110 is configured to generate a significant photocurrent Ii in response to incident radiation having a wavelength λι in the range of λΓι. The first detector 112-1 is configured to receive the incident radiation by way of the window 114 of the sandwich detector 110. The first detector 110 may be configured to generate a significant photocurrent Ii with responsivity greater than a defined threshold (e.g., 0.005 Amp/Watt) for incident radiation having a wavelength λι in the range of λΓι. As an example, the first detector 112-1 may be a silicon-based photodiode configured to generate a significant photocurrent Ii for incident radiation having a wavelength from about 200nm to about llOOnm.
[ 0020 ] The second detector 112-2 of the sandwich detector 110 is configured to generate a significant photocurrent I2 in response to incident radiation having a wavelength λ2 in the range of λΓ2. The second detector 112-2 is configured to receive this radiation by way of the window 114 and the first detector 112-1. The second detector 112-2 is configured to generate a significant photocurrent I2 with responsivity greater than a defined threshold (e.g., 0.005 Amp/Watt) for incident radiation having a wavelength λ2 in the range of λΓ2. As an example, the second detector 112-2 may be a germanium-based photodiode configured to generate a significant photocurrent I2 for incident radiation having a wavelength from about 700nm to about 1800nm.
[ 0021 ] The first amplifier 120-1 may be configured as a transimpedance amplifier. That is, the first amplifier 120-1 may be configured to receive the first photocurrent Ii generated by the first detector 112-1 in response to incident radiation with a wavelength λι within the range of λΓι, and generate a corresponding voltage Vi from the photocurrent Ii based on a defined transimpedance gain.
[ 0022 ] Similarly, the second amplifier 120-2 may also be configured as a transimpedance amplifier. That is, the second amplifier 120-2 may be configured to receive the second photocurrent I2 generated by the second detector 112-2 in response to incident radiation with a wavelength λ2 within the range of λΓ2, and generate a corresponding voltage V2 from the photocurrent I2 based on a defined transimpedance gain.
[ 0023 ] The summing device 130 is configured to combine or sum the voltages Vi and V2 together to generate an output voltage Vout for the optical detector 100. Because the sandwich detector 110 has distinct detectors 112-1 and 112-2 capable of generating significant photocurrents in response to incident radiation of distinct wavelength bands, the output voltage Vout is consequently responsive to wideband incident radiation. Accordingly, the optical detector 100 has the advantage of providing wideband detection without the use of a switching device to select the appropriate detector, as commonly employed in prior art wideband detectors. Additionally, because the sandwich detector 110 uses photodiodes, it is not prone to significant noise, as is a pyro electric detector.
[ 0024 ] Although, in this example, the sandwich detector 110 comprises two distinct detectors 112-1 and 112-2, it shall be understood that the sandwich detector 110 may comprise more than two detectors. For example, another embodiment may comprise three distinct detectors configured in a substantially vertically stacked orientation. As an example, such sandwich detector may comprise three distinct photodiodes based on silicon, germanium, and indium- gallium-arsenide, so that the optical detector is able to detect incident radiation having a wavelength between about 200nm and about 2600nm. Another embodiment may comprise four distinct detectors configured in a substantially vertically stacked orientation. As an example, such sandwich detector may comprise four distinct photodiodes based on silicon, germanium, indium-gallium- arsenide, and lead- sulfide, so that the optical detector is able to detect incident radiation having a wavelength between about 200nm and about 3500nm.
[ 0025 ] Various combinations of distinct detectors may be implemented in a sandwich detector in order to provide the optical detector with a specified wavelength band detection capability. Further, as exemplified, it shall be understood that the wavelength detection ranges of the distinct detectors in a sandwich detector may overlap. In the overlap region, the optical detector has a responsivity that is substantially the sum of the responsivity of the individual detectors in that region. Thus, in the overlap region, the optical detector provides increased responsivity for better detection of low power signals.
[ 0026 ] FIG. 2 illustrates a block diagram of another exemplary wideband wavelength optical detector 200 in accordance with another aspect of the disclosure. The optical detector 200 may be an exemplary more detailed implementation of the optical detector 100, previously discussed. In summary, the optical detector 200 comprises a sandwich detector including distinct detectors (e.g., photodiodes) configured to detect incident radiation in distinct wavelength bands, respectively. The optical detector further comprises user- configurable gain amplifiers configured to amplify the photocurrents generated by the distinct detectors of the sandwich detector, respectively. Additionally, the optical detector 200 comprises a pair of cascaded inverting amplifiers configured to sum the voltages generated at the outputs of the amplifiers, and produce an output voltage for the optical detector 200.
[ 0027 ] In particular, the optical detector 200 comprises a sandwich detector 210, a first amplifier 220-1 and corresponding circuitry, such as gain select 222-1 and resistors R11-R14, for providing gain adjustment of the first amplifier by a user, and a second amplifier 220-2 and corresponding circuitry, such as gain select 222-2 and resistors R21-R24, for providing gain adjustment of the second amplifier by a user. Additionally, the optical detector 200 comprises a first inverting amplifier 230 and gain setting and summing circuitry, such as resistors R32, R34, and R36. Similarly, the optical detector 200 comprises a second inverting amplifier 240 and gain setting circuitry, such as R42 and R44. [ 0028 ] More specifically, the sandwich detector 210 comprises a first detector 212-1, a second detector 212-2, and a window 214, all of which are configured substantially in a vertically stacked orientation. Similar to the previous embodiment, the first detector 212-1 is configured to generate a significant photocurrent Ii (e.g., with a responsivity > 0.005 Amp/Watt) in response to incident radiation with a wavelength λι in a range of λΓι. The first detector 212-1 is configured to receive incident radiation λι by way of the window 214. Similarly, the second detector 212-2 is configured to generate a significant photocurrent I2 (e.g., with a responsivity > 0.005 Amp/Watt) in response to incident radiation with a wavelength λ2 in a range of λΓ2. The second detector 212-2 is configured to receive the incident radiation λ2 by way of the window 214 and the first detector 212-1. As discussed with respect to the previous embodiment, it shall be understood that the sandwich detector 210 may comprise more than two distinct detectors.
[ 0029 ] The first and second detectors 212-1 and 212-2 have a grounded terminal coupled together and to positive input terminals of the first and second amplifiers 220-1 and 220-2. The terminal of the first detector 212-1 at which the photocurrent Ii is generated is coupled to a negative input terminal of the first amplifier 220-1. Similarly, the terminal of the second detector 212-2 at which the photocurrent I2 is generated is coupled to a negative input terminal of the second amplifier 220-2. The first and second amplifiers 220-1 and 220-2 may be configured as transimpedance amplifiers to generate voltages Vi and V2 by applying transimpedance gains on the first and second photocurrents Ii and I2, respectively.
[ 0030 ] The optical detector 200 includes circuitry to allow a user to set the transimpedance gains of the first and second amplifiers 220-1 and 220-2. For instance, with regard to the first amplifier 220-1, the optical detector 200 comprises a first bank of resistors R11-R14 and a first gain select circuit 222-1, both coupled in series between the output and the negative input of the first amplifier 220-1 in a feedback configuration. The first gain select circuit 222-1 operates as a multiplexer configured to couple one or more of the resistors Rll- R14 to the negative input of the first amplifier 220-1 based on a user input. The transimpedance gain of the first amplifier 220-1 is based on which one or more of the resistors R11-R14 are coupled to the negative input and output of the first amplifier. The resistors R11-R14 may be configured as a binary (e.g., 10kQ, 20kQ, 40kQ, and 80kQ), decimal (e.g., 10kQ, 100kQ, 1ΜΩ, and 10ΜΩ), or other type of resistor bank.
[ 0031 ] Similarly, with regard to the second amplifier 220-1, the optical detector 200 comprises a second bank of resistors R21-R24 and a second gain select circuit 222-2, both coupled in series between the output and the negative input of the second amplifier 220-2 in a feedback configuration. The second gain select circuit 222-2 operates as a multiplexer configured to couple one or more of the resistors R21-R24 to the negative input of the second amplifier 220-2 based on a user input. The transimpedance gain of the second amplifier 220-2 is based on which one or more of the resistors R21-R24 is coupled to the negative input and output of the second amplifier. The resistors R21-R24 may be configured as a binary (e.g., 10kQ, 20kQ, 40kQ, and 80kQ), decimal (e.g., 10kQ, 100kQ, 1ΜΩ, and 10ΜΩ), or other type of resistor bank.
[ 0032 ] The output of the first amplifier 220-1, at which the first voltage Vi is generated, is coupled to a negative input of the first inverting amplifier 230 by way of resistor R32. Similarly, the output of the second amplifier 220-2, at which the second voltage V2 is generated, is coupled to the negative input of the first inverting amplifier 230 by way of resistor R34. Accordingly, the sum of the first and second voltages Vi and V2 is generated at the negative input of the first inverting amplifier 230.
[ 0033 ] The first inverting amplifier 230 applies respective gains to the voltages Vi and V2 based on the ratio of resistor R36 over R32 and the ratio of resistor R36 over R34, respectively. More specifically, the voltage at the output of the first inverting amplifier 230 may be equal to - (R36/R32 * Vi + R36/R34 * V2). The second inverting amplifier 240 applies a gain to the voltage at the output of the first inverting amplifier 230 based on a ratio of resistor R44 over R42 to generate an output voltage Vout for the optical detector 200. More specifically, the output voltage Vout may be equal to R44/R42 * (R36/R32 * Vi + R36/R34 * V2). If, for example, all of the resistors R32, R34, R36, R42, and R2 have substantially the same resistance, then the output voltage Vout may be equal to Vi + V2, where Vi is a function of the first photocurrent Ii (e.g., Vi = R of bank R11-R14 * Ii) and V2 is a function of the second photocurrent I2 (e.g., V2 = R of bank R21-R24 * I2).
[ 0034 ] As with the previous embodiment, various combinations of distinct detectors may be implemented in the sandwich detector in order to provide the optical detector with a specified wavelength band detection capability. Further, as exemplified, it shall be understood that the wavelength detection ranges of the distinct detectors in a sandwich detector may overlap. In the overlap region, the optical detector has a responsivity that is substantially the sum of the responsivity of the individual detectors in that region. Thus, in the overlap region, the optical detector provides increased responsivity for better detection of low power signals.
[ 0035 ] FIG. 3 illustrates a flow diagram of an exemplary method 300 of calibrating the exemplary wideband optical detector in accordance with another aspect of the disclosure. In summary, the method 300 is configured to generate a table of responsivity for different input wavelengths optical signals. When using the optical detector, a user may be able to determine the input power of the signal applied to the detector using the table. The table may be stored internally in the detector through the use of a non-volatile memory, or the table may be stored in a compact disk or the like, which is provided to the user upon acquiring the optical detector.
[ 0036 ] In particular, according to the method 300, a variable i is set to zero (0), which keep tracks of the current input wavelength signal from which the responsivity of the detector is being measured (block 302). Then, according to the method 300, an optical signal with a wavelength Xi is applied to the input of the wideband optical detector (block 304). The power of the input optical signal is measured with a calibrated device (block 306).
[ 0037 ] Also, a measurement of the photocurrent current or voltage at the output of the detector is taken (block 308). For example, the photocurrent may be measured directly. As an example, in the case where the current wavelength Xi of the input signal falls within the non- overlapping range of the first detector of the sandwich detector, the photocurrent is substantially Ii. Similarly, in the case where the current wavelength Xi of the input signal falls within the non- overlapping range of the second detector of the sandwich detector, the photocurrent is substantially I2. Further, in the case where the current wavelength Xi of the input signal falls within the overlapping range of the first and second detectors of the sandwich detector, the photocurrent is substantially Ii + I2. The applicable photocurrent may also be measured indirectly by measuring the output voltage Vout, since the output voltage Vout is a function of the applicable photocurrents and the aggregate gain applied to the photocurrents.
[ 0038 ] Once the power of the input optical signal and corresponding photocurrent are determined, they are recorded in a responsivity table (block 310). As previously discussed, the optical detector may include an internal memory, such as a non-volatile memory, in which the table may be stored. Alternatively, or in addition to, the responsivity table may be recorded on a compact disk or other portable memory, and provided to a user upon acquiring the optical detector.
[ 0039 ] Then, according to the method 300, the variable i for keeping track of the current wavelength Xi during the calibration procedure is incremented (block 312). Then, the incremented variable i is then compared to the number N of distinct wavelengths for which the optical detector is being calibrated (block 314). If there are remaining wavelengths over which the optical detector is to be calibrated (e.g., i <N), then the operations indicated in blocks 304 to 314 are repeated again. On the other hand, if there are no remaining wavelengths over which the optical detector is to be calibrated (e.g., i =N), then the responsivity table is complete and may be stored in the appropriate memory device as discussed above (block 316).
[ 0040 ] FIG. 4 illustrates a graph of an exemplary responsivity response of an exemplary wideband optical detector in accordance with another aspect of the disclosure. In particular, this is an example of a wideband optical detector that employs a sandwich detector comprising a first detector being a silicon-based photodiode and a second detector being a germanium-based photodiode. As previously mentioned, a silicon-based detector is capable of detecting or generating significant photocurrent (e.g., with a responsivity > 0.005 Amp/Watt) in response to incident radiation with a wavelength in the range of 200nm to about llOOnm. Similarly, a germanium-based detector is capable of detecting or generating significant photocurrent in response to incident radiation with a wavelength in the range of 700nm to about 1800nm.
[ 0041 ] Accordingly, an optical detector that employs a sandwich detector with a first detector being a silicon-based detector and a second detector being a germanium-based detector in accordance with the teachings herein will have a significant responsivity (e.g., responsivity > 0.005 Amp/Watt) for wavelengths extending from 200nm to 1800nm. Thus, such an optical detector is capable of wideband applications without the need of a switch for selecting the appropriate detector and without the excess noise inherent in pyro electric detectors. Thus, the optical detector, in accordance with the teachings herein, serves as a useful measurement equipment for wideband optical detection applications and usability.
[ 0042 ] While the invention has been described in connection with various embodiments, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within the known and customary practice within the art to which the invention pertains.

Claims

What is claimed is:
1. An optical detector, comprising:
a sandwich detector comprising:
a window;
a first detecting element configured to generate a first photocurrent in response to first incident radiation having a first wavelength within a first wavelength range, wherein the first detecting element is configured to receive the first incident radiation by way of the window; and
a second detecting element configured to generate a second photocurrent in response to second incident radiation having a second wavelength within a second wavelength range that is different than the first wavelength range, wherein the second detecting element is configured to receive the second incident radiation by way of the window and the first detecting element;
a first amplifier configured to generate a first signal based on the first photocurrent;
a second amplifier configured to generate a second signal based on the second photocurrent; and
a summing device configured to generate an output signal based on the first and second signals.
2. The optical detector of claim 1, wherein the first amplifier comprises a transimpedance amplifier, and wherein the first signal comprises a first voltage.
3. The optical detector of claim 2, wherein the first amplifier comprises a user-adjustable transimpedance gain.
4. The optical detector of claim 2, further comprising:
a resistor bank including a plurality of resistors; and
a multiplexer configured to couple one or more of the resistors to the first amplifier in response to a user input, wherein a transimpedance gain of the first amplifier is a function of the one or more of the resistors coupled to the first amplifier.
5. The optical detector of claim 2, wherein the second amplifier comprises a transimpedance amplifier, and wherein the second signal comprises a second voltage.
6. The optical detector of claim 5, wherein the second amplifier comprises a user-adjustable transimpedance gain.
7. The optical detector of claim 5, further comprising:
a resistor bank including a plurality of resistors; and
a multiplexer configured to couple one or more of the resistors to the second amplifier in response to a user input, wherein a transimpedance gain of the second amplifier is a function of the one or more of the resistors coupled to the second amplifier.
8. The optical detector of claim 1, wherein the summing device comprises a first inverting amplifier including a negative input terminal configured to receive the first and second signals.
9. The optical detector of claim 8, further comprising a second inverting amplifier coupled to an output of the first inverting amplifier, wherein the output signal is generated at an output of the second inverting amplifier.
10. The optical detector of claim 1, wherein the first detecting element comprises one of the following:
a silicon-based photodiode;
a germanium-based photodiode;
an indium-gallium-arsenide-based photodiode; or
a lead-sulfide-based photodiode.
11. The optical detector of claim 10, wherein the second detecting element comprises one of the following:
a silicon-based photodiode;
a germanium-based photodiode;
an indium-gallium-arsenide-based photodiode; or
a lead-sulfide-based photodiode.
12. The optical detector of claim 1, wherein the first or second detecting element is configured to generate the first or second photocurrent with responsivity greater than 0.005 Amp/Watt.
13. An optical detector, comprising:
a sandwich detector comprising:
a first detecting element configured to generate a first photocurrent in response to first incident radiation with a first wavelength within a first wavelength range; and
a second detecting element configured to generate a second photocurrent in response to second incident radiation with a second wavelength within a second wavelength range that is different than the first wavelength range; and
a device configured to generate a signal based on the first and second photocurrents.
14. The optical detector of claim 13, wherein the device comprises a summing device.
15. The optical detector of claim 13, further comprising:
a first transimpedance amplifier configured to generate a first voltage based on the first photocurrent; and
a second transimpedance amplifier configured to generate a second voltage based on the second photocurrent.
16. The optical detector of claim 15, wherein the device is configured to generate the signal based on the first and second voltages.
17. The optical detector of claim 15, wherein the signal comprises an output voltage, and wherein the device comprises a summing device configured to generate the output voltage by summing the first and second voltages.
18. The optical detector of claim 15, wherein the first and second transimpedance amplifiers comprise first and second user-adjustable transimpedance gains.
19. The optical detector of claim 13, wherein the first or second detecting element is configured to generate the first or second photocurrent with responsivity greater than a defined responsivity threshold.
20. An optical detector, comprising:
a sandwich detector comprising:
a window;
a first detecting element configured to generate a first photocurrent in response to first incident radiation with a first wavelength within a first wavelength range, wherein the first detecting element is configured to receive the first incident radiation by way of the window; and
a second detecting element configured to generate a second photocurrent in response to second incident radiation with a second wavelength within a second wavelength range that is different than the first wavelength range, wherein the second detecting element is configured to receive the second incident radiation by way of the window; and
a device configured to generate a signal based on the first and second photocurrents.
PCT/US2012/052905 2012-08-29 2012-08-29 System and method of providing wideband wavelength optical detection using sandwich detector WO2014035389A1 (en)

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