WO2017205892A1 - Améliorations de lignes à retard optique - Google Patents

Améliorations de lignes à retard optique Download PDF

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Publication number
WO2017205892A1
WO2017205892A1 PCT/AU2017/000121 AU2017000121W WO2017205892A1 WO 2017205892 A1 WO2017205892 A1 WO 2017205892A1 AU 2017000121 W AU2017000121 W AU 2017000121W WO 2017205892 A1 WO2017205892 A1 WO 2017205892A1
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WIPO (PCT)
Prior art keywords
optical
optical signal
optical delay
delay
delay line
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PCT/AU2017/000121
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English (en)
Inventor
Roland FLEDDERMANN
Woei Ming LEE
Jong Chow
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Australian National University
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Australian National University
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Priority claimed from AU2016902093A external-priority patent/AU2016902093A0/en
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Publication of WO2017205892A1 publication Critical patent/WO2017205892A1/fr
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2861—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using fibre optic delay lines and optical elements associated with them, e.g. for use in signal processing, e.g. filtering

Definitions

  • the present invention relates generally to improvements in optical delay lines.
  • the present invention relates to an optical delay system and method of controlling optical delay in an optical delay line system.
  • Optical delay lines are utilised in systems for measuring laser pulses and for imaging.
  • High speed temporal optical delay lines are widely used in many optical systems, including, for example in systems that utilise ultrafast pulse measurement, Doppler phase shifting and optical coherence tomography.
  • Rotating optical delay lines achieve much higher speeds.
  • There are two classes of rotating delay lines including small angle tilted mirrors and multi-facet rotating mirrors.
  • Multi-facet mirror scanners using cube mirrors or mirror arrays operate with higher duty cycle (single direction) and linearity at a lower repetition rate.
  • mirror arrays achieve high repetition rates of a few kHz accompanied by high linearity, they remain bulky, requiring high torque motors to drive them.
  • Repetition rates in rotating mirror scanners are ultimately limited by the size of the mirror, which dictates the number of facets (n) covering a given circumference (2m).
  • smaller mirrors also have limited scan depth and repetition rates.
  • TD OCT video rate time domain
  • SD spectral domain
  • FD Fourier domain
  • the speed depends largely on the sweeping frequency of a swept source laser and frame rate of line charged coupled device (CCD) capable of reaching hundreds of kHz scan rates.
  • CCD line charged coupled device
  • Current commercial SD OCT systems based on swept sources generally operate between 4 to 400 kHz. Even the most sophisticated approaches so far using mirror arrays are only able to deliver 4 kHz scan rates, which is considered too low for video rate time domain OCT systems.
  • a method for ultra-fast optical delay modulation with a repetition rate of up to 41 kHz while maintaining high linearity and duty cycle is provided.
  • a method for further improving the scan rate or scan depth of the optical delay line system by cascading multiple reflections or transmissions of optical beams, or spatially controlling reflections or transmissions of optical beams, directed to and received from one or more optical delay elements (e.g. on a rotating phase plate) as per the methods and systems disclosed herein.
  • an apparatus or system for implementing any one of the aforementioned methods there is provided an apparatus or system for implementing any one of the aforementioned methods.
  • a computer program product including a computer readable medium having recorded thereon a computer program for implementing any one of the methods described herein.
  • the present disclosure provides an optical delay line system comprising: a plurality of cascading delay lines adapted for use in an optical system, wherein a first cascading delay line of at least two of the plurality of cascading delay lines is arranged to: direct the first optical signal towards a first optical delay element; and receive a second optical signal, wherein the second optical signal is a version of the first optical signal that has acquired a first time-dependent optical delay introduced by the first optical delay element; wherein a second cascading delay line of at least two of the plurality of cascading delay lines is arranged to: direct the second optical signal towards a second optical delay element; and receive a third optical signal, wherein the third optical signal is a version of the second optical signal that has acquired a second time-dependent optical delay introduced by the second optical delay element, and direct the third optical signal to either a further cascading delay line of the plurality of cascading delay lines or to the optical system.
  • the present disclosure provides a method of controlling optical delay in an optical delay line system for use in an optical system, the method comprising the steps of: receiving a first optical signal from an optical system; directing the first optical signal towards a first optical delay element, receiving a second optical signal, wherein the second optical signal is a version of the first optical signal that has acquired a first time- dependent optical delay introduced by the first optical delay element; directing the second optical signal towards a second optical delay element; receiving a third optical signal, wherein the third optical signal is a version of the second optical signal that has acquired a second time- dependent optical delay introduced by the second optical delay element and directing the third optical signal towards a further optical delay element or the optical system.
  • FIG. 1A and 1 B form a schematic block diagram of a general purpose computer system upon which arrangements described can be practiced;
  • FIG. 1 depicts a process according to an embodiment of the present invention
  • Figs 3A to 3D depict a spiral phase plate, intensity distribution obtained by reflecting a Gaussian laser beam off this phase plate resulting in a Laguerre-Gaussian beam, a segment (element) of the phase plate and low coherence interference fringes obtained from using the phase plate as a delay line respectively;
  • Fig 4A depicts a Gaussian beam on top of a 4-sector spiral phase plate, with an example of a Laguerre Gaussian Beam which can be obtained by reflecting a Gaussian beam off a spiral phase plate at the bottom;
  • FIGs 4B to 4G depict synchronous and asynchronous modes of operation according to embodiments of the present invention.
  • Fig 5A shows an optical delay line system according to an embodiment of the present invention
  • Fig 5B shows an optical coherence tomography system with the optical delay line system of Fig 5A according to an embodiment of the present invention
  • Figs 6A-6F show various results of an optical delay line system operating in synchronous and asynchronous modes according to embodiments of the present invention
  • Figs 7A and 7B show the results of a video rate OCT imaging scan according to an embodiment of the present invention
  • Figs 8A-8D show the results of a further scan according to an embodiment of the present invention.
  • Fig 9 shows a transmissive rotating phase plate used with optical delay lines in accordance with an embodiment of the present invention
  • Figures 10A and 10B show examples of a linear optical delay element transport system used with optical delay lines in accordance with embodiments of the present invention. Detailed Description including Best Mode
  • FIGs. 1A and 1 B depict a general-purpose computer system 1300, upon which the various arrangements described can be practiced.
  • the computer system 1300 includes: a computer module 1301 ; input devices such as a keyboard 1302, a mouse pointer device 1303, a scanner 1326, a camera 1327, an imaging system (such as an OCT system for example) 1382 and a
  • An external Modulator-Demodulator (Modem) transceiver device 1316 may be used by the computer module 1301 for communicating to and from a communications network 1320 via a connection 1321.
  • the communications network 1320 may be a wide-area network (WAN), such as the Internet, a cellular telecommunications network, or a private WAN.
  • the modem 1316 may be a traditional "dial-up" modem.
  • the modem 1316 may be a broadband modem.
  • a wireless modem may also be used for wireless connection to the communications network 1320.
  • the imaging system 1382 such as an OCT system, may incorporate various elements of the general-purpose computer system therein rather than being attached to the general-purpose computer system.
  • the computer module 1301 typically includes at least one processor unit 1305, and a memory unit 1306.
  • the memory unit 1306 may have semiconductor random access memory (RAM) and semiconductor read only memory (ROM).
  • the computer module 1301 also includes a number of input/output (I/O) interfaces including: an audio-video interface 1307 that couples to the video display 1314, loudspeakers 1317 and
  • the modem 1316 may be incorporated within the computer module 1301 , for example within the interface 1308.
  • the computer module 1301 also has a local network interface 131 1 , which permits coupling of the computer system 1300 via a connection 1323 to a local-area communications network 1322, known as a Local Area Network (LAN).
  • LAN Local Area Network
  • the local communications network 1322 may also couple to the wide network 1320 via a connection 1324, which would typically include a so-called "firewall” device or device of similar functionality.
  • the local network interface 131 1 may comprise an Ethernet circuit card, a Bluetooth ® wireless arrangement or an IEEE 802.1 1 wireless arrangement; however, numerous other types of interfaces may be practiced for the interface 131 1.
  • the I/O interfaces 1308 and 1313 may afford either or both of serial and parallel connectivity, the former typically being implemented according to the Universal Serial Bus (USB) standards and having corresponding USB connectors (not illustrated).
  • Storage devices 1309 are provided and typically include a hard disk drive (HDD) 1310. Other storage devices such as a floppy disk drive and a magnetic tape drive (not illustrated) may also be used.
  • An optical disk drive 1312 is typically provided to act as a non-volatile source of data.
  • Portable memory devices such optical disks (e.g., CD-ROM, DVD, Blu-ray DiscTM), USB-RAM, portable, external hard drives, and floppy disks, for example, may be used as appropriate sources of data to the system 1300.
  • the components 1305 to 1313 of the computer module 1301 typically communicate via an interconnected bus 1304 and in a manner that results in a conventional mode of operation of the computer system 1300 known to those in the relevant art.
  • the processor 1305 is coupled to the system bus 1304 using a connection 1318.
  • the memory 1306 and optical disk drive 1312 are coupled to the system bus 1304 by connections 1319. Examples of computers on which the described arrangements can be practised include IBM-PC's and compatibles, Apple MacTM or like computer systems.
  • the control methods described herein may be implemented using the computer system 1300 wherein the processes of Fig. 2 and associated control methods, to be described, may be implemented as one or more software application programs 1333 executable within the computer system 1300.
  • the steps of the control methods are effected by instructions 1331 (see Fig. 1 B) in the software 1333 that are carried out within the computer system 1300.
  • the software instructions 1331 may be formed as one or more code modules, each for performing one or more particular tasks.
  • the software may also be divided into two separate parts, in which a first part and the corresponding code modules performs the control methods and a second part and the corresponding code modules manage a user interface between the first part and the user.
  • the software may be stored in a computer readable medium, including the storage devices described below, for example.
  • the software is loaded into the computer system 1300 from the computer readable medium, and then executed by the computer system 1300.
  • a computer readable medium having such software or computer program recorded on the computer readable medium is a computer program product.
  • the use of the computer program product in the computer system 1300 preferably effects an advantageous apparatus for controlling an optical delay line system.
  • the software 1333 is typically stored in the HDD 1310 or the memory 1306.
  • the software is loaded into the computer system 1300 from a computer readable medium, and executed by the computer system 1300.
  • the software 1333 may be stored on an optically readable disk storage medium (e.g., CD-ROM) 1325 that is read by the optical disk drive 1312.
  • a computer readable medium having such software or computer program recorded on it is a computer program product.
  • the use of the computer program product in the computer system 1300 preferably effects an apparatus for controlling an optical delay line system.
  • the application programs 1333 may be supplied to the user encoded on one or more CD-ROMs 1325 and read via the corresponding drive 1312, or alternatively may be read by the user from the networks 1320 or 1322. Still further, the software can also be loaded into the computer system 1300 from other computer readable media.
  • Computer readable storage media refers to any non-transitory tangible storage medium that provides recorded instructions and/or data to the computer system 1300 for execution and/or processing. Examples of such storage media include floppy disks, magnetic tape, CD-ROM, DVD, Blu-rayTM Disc, a hard disk drive, a ROM or integrated circuit, USB memory, a magneto- optical disk, or a computer readable card such as a PCMCIA card and the like, whether or not such devices are internal or external of the computer module 1301.
  • Examples of transitory or non-tangible computer readable transmission media that may also participate in the provision of software, application programs, instructions and/or data to the computer module 1301 include radio or infra-red transmission channels as well as a network connection to another computer or networked device, and the Internet or Intranets including e-mail transmissions and information recorded on Websites and the like.
  • GUIs graphical user interfaces
  • a user of the computer system 1300 and the application may manipulate the interface in a functionally adaptable manner to provide controlling commands and/or input to the applications associated with the GUI(s).
  • Other forms of functionally adaptable user interfaces may also be implemented, such as an audio interface utilizing speech prompts output via the loudspeakers 1317 and user voice commands input via the microphone 1380.
  • Fig. 1 B is a detailed schematic block diagram of the processor 1305 and a
  • the memory 1334 represents a logical aggregation of all the memory modules (including the HDD 1309 and semiconductor memory 1306) that can be accessed by the computer module 1301 in Fig. 1A.
  • a power-on self-test (POST) program 1350 executes.
  • the POST program 1350 is typically stored in a ROM 1349 of the semiconductor memory 1306 of Fig. 1A.
  • a hardware device such as the ROM 1349 storing software is sometimes referred to as firmware.
  • the POST program 1350 examines hardware within the computer module 1301 to ensure proper functioning and typically checks the processor 1305, the memory 1334 (1309, 1306), and a basic input-output systems software (BIOS) module 1351 , also typically stored in the ROM 1349, for correct operation. Once the POST program 1350 has run successfully, the BIOS 1351 activates the hard disk drive 1310 of Fig. 1 A.
  • BIOS basic input-output systems software
  • Activation of the hard disk drive 1310 causes a bootstrap loader program 1352 that is resident on the hard disk drive 1310 to execute via the processor 1305.
  • the operating system 1353 is a system level application, executable by the processor 1305, to fulfil various high level functions, including processor management, memory management, device management, storage management, software application interface, and generic user interface.
  • the operating system 1353 manages the memory 1334 (1309, 1306) to ensure that each process or application running on the computer module 1301 has sufficient memory in which to execute without colliding with memory allocated to another process.
  • the different types of memory available in the system 1300 of Fig. 1A must be used properly so that each process can run effectively. Accordingly, the aggregated memory 1334 is not intended to illustrate how particular segments of memory are allocated (unless otherwise stated), but rather to provide a general view of the memory accessible by the computer system 1300 and how such is used.
  • the processor 1305 includes a number of functional modules including a control unit 1339, an arithmetic logic unit (ALU) 1340, and a local or internal memory 1348, sometimes called a cache memory.
  • the cache memory 1348 typically includes a number of storage registers 1344 - 1346 in a register section.
  • One or more internal busses 1341 functionally interconnect these functional modules.
  • the processor 1305 typically also has one or more interfaces 1342 for communicating with external devices via the system bus 1304, using a connection 1318.
  • the memory 1334 is coupled to the bus 1304 using a connection 1319.
  • the application program 1333 includes a sequence of instructions 1331 that may include conditional branch and loop instructions.
  • the program 1333 may also include data 1332 which is used in execution of the program 1333.
  • the instructions 1331 and the data 1332 are stored in memory locations 1328, 1329, 1330 and 1335, 1336, 1337,
  • a particular instruction may be stored in a single memory location as depicted by the instruction shown in the memory location 1330.
  • an instruction may be segmented into a number of parts each of which is stored in a separate memory location, as depicted by the instruction segments shown in the memory locations 1328 and 1329.
  • the processor 1305 is given a set of instructions which are executed therein.
  • the processor 1305 waits for a subsequent input, to which the processor 1305 reacts to by executing another set of instructions.
  • Each input may be provided from one or more of a number of sources, including data generated by one or more of the input devices 1302, 1303, data received from an external source across one of the networks 1320, 1302, data retrieved from one of the storage devices 1306, 1309 or data retrieved from a storage medium 1325 inserted into the corresponding reader 1312, all depicted in Fig. 1A.
  • the execution of a set of the instructions may in some cases result in output of data. Execution may also involve storing data or variables to the memory 1334.
  • the disclosed optical delay line control arrangements use input variables 1354, which are stored in the memory 1334 in corresponding memory locations 1355, 1356, 1357.
  • the optical delay line control arrangements produce output variables 1361 , which are stored in the memory 1334 in corresponding memory locations 1362, 1363, 1364.
  • variables 1358 may be stored in memory locations 1359, 1360, 1366 and 1367.
  • each fetch, decode, and execute cycle comprises:
  • a fetch operation which fetches or reads an instruction 1331 from a memory location 1328, 1329, 1330;
  • a further fetch, decode, and execute cycle for the next instruction may be executed.
  • a store cycle may be performed by which the control unit 1339 stores or writes a value to a memory location 1332.
  • Each step or sub-process in the processes of Fig 2 and associated control methods is associated with one or more segments of the program 1333 and is performed by the register section 1344, 1345, 1347, the ALU 1340, and the control unit 1339 in the processor 1305 working together to perform the fetch, decode, and execute cycles for every instruction in the instruction set for the noted segments of the program 1333.
  • optical delay line control method may alternatively be implemented in dedicated hardware such as one or more integrated circuits performing the functions or sub functions of optical delay line control.
  • dedicated hardware may include graphic processors, digital signal processors, or one or more microprocessors and associated memories.
  • a micro-machined structured phase plate is integrated with cascading optical delay lines into a low-coherence interferometer.
  • a ten-fold increase of rate of temporal modulation into a 40 kHz regime is demonstrated.
  • the rate of the temporal modulation is increased with minimal alteration of the reference arm length.
  • phase plate The concept of tunable temporal modulation of a phase plate is described along with associated references to spatial modulation.
  • the orbital angular momentum of a spiral phase beam relies on the overall phase shift acquired around the circumference of the beam.
  • the phase shift is proportional to the physical height of the spiral phase segment upon which the beam is being directed.
  • a multi-step spiral phase plate may be constructed that includes a collection of linear ramps.
  • Figure 3a shows a micro-machined spiral phase plate 301 .
  • Figure 3b shows spatial modulation of the spiral phase plate with distinct annular intensity rings.
  • Figure 3c shows a zoomed in image of a segment 303 of the phase plate.
  • Figure 3d shows low coherence interference fringes from rotating the spiral phase plate at 300 Hz.
  • a broad illumination from an optical source of a known multi-step spiral phase plate, shown in Figure 3a, fabricated using a nano-lathe machine provides an overall linear delay line around the circumference of the beam that upon reflection changes a Gaussian beam into an LG beam with an annular intensity pattern as shown in Figure 3b.
  • phase plate imparts a given orbital angular momentum of kf to the beam, where k is the helicity or winding and f is the reduced Planck constant.
  • a known imaging system using an optical beam focused onto a single segment of a rotating spiral plate shown in Figure 3c, will experience a fixed phase shift over multiple segments over the circumference of the phase plate.
  • Each phase plate segment m has a physical height h that corresponds to an integer multiple n of the wavelength of the incident light A.
  • the overall scan rate is the product of the rotation rate f rot and the number of segments k.
  • Figure. 3d shows that known scanning systems using a single beam standard spiral phase plate of 128 segments could potentially reach a 45 kHz scan rate but are severely limited in depth scanning.
  • the temporal modulation creates a time varying phase shift ⁇ ⁇ which now depends on the time t instead of the angular position on the phase plate ⁇ .
  • the angular position is replaced with the angular rotation rate multiplied by the time oj rot f.
  • the configuration of a single reflection is limiting, even with large number of smaller elements.
  • the overall optical path length is then restricted by the physical height of each segment where there is a limited scan depth and repetition rates, as Figure 3d.
  • d(f) denotes the path length at any given time t
  • frac[x] represents the fractional part of x.
  • Figure 4a shows a rotating phase plate 401 having four ramp surfaces (403A - 403D) around its circumference. Each ramp surface varies around the circumference of the phase plate between a minimum height and a maximum height, where each ramp surface has the same minimum and maximum heights.
  • Figure. 4b and 4c show two timing examples, the synchronous (4b) and asynchronous (4c) timing using two beams.
  • the incident beam undergoes twice the amount of optical delay before returning back (and being modulated with a sample signal) as indicated by the ramp plot.
  • synchronous timing indicates an increased scanning depth.
  • the asynchronous positioning means that the incident beam undergoes two different phase delays which increases the scan rate instead, as shown in the ramp plots in Figure 4c.
  • figures 4b and 4c show a schematic illustrating a multiple pass approach for a single optical beam being applied to the rotating phase plate of Figure 4a.
  • Figure 4c shows an
  • asynchronous scan of the phase ramp where the optical beam makes two passes to the phase plate, where each pass has an asynchronous position such that the initial beam is applied to a first position on the edge of a first phase ramp (or segment) and the reflected beam is applied to a second position on an edge of a second (i.e. different) phase ramp (or segment).
  • the first and second positions are not the same such that ⁇ h 2 .
  • h 2 2, i.e. the second reflection point is half-way along the ramp for a linear ramp.
  • each delay would be 1/n further along the ramp, i.e.
  • h n h n tox *n.
  • the synchronous phase step provides double (n-times for n cascaded delays) depth at the same scan rate, whereas asynchronous positioning produces twice (n-times for n cascaded delays) the repetition rate.
  • FIGs 4D to 4G show further details of the timing examples shown in Figures 4B and 4C.
  • a fibre based cascading delay line system 501 is described according to an
  • the optical delay line system may, in any part of the system, use an optical medium other than optical fibres.
  • the optical delay line system may use air as the optical medium, where the beam orientation and direction is controlled to ensure that it is captured by the components of the system.
  • a double cascaded delay line system is described which is scalable by the number of delays.
  • a portion of an optical beam being used in an optical system is fed as an input optical signal 507 into the optical delay line system 501.
  • the input optical signal 507 is directed to the first optical delay line 503A.
  • the input optical signal 507 is directed to a first optical circulator 509A of the first optical delay line 503A.
  • the optical circulator 509A directs the input signal 507 to a first focussing optic 51 1A.
  • the focussing optic 51 1 A includes two lenses that are used to focus the input signal 507 onto elements 513x (i.e. 513A, 513B etc.) of the phase plate 515.
  • the focussing optic 51 1A also receives a first reflected light beam reflected off an element of the phase plate.
  • the first reflected light beam (the reflected input signal) is directed back through the first optical circulator 509A towards the second optical delay line 503B.
  • the first reflected light beam is directed to a second optical circulator 509B of the second optical delay line 503B.
  • the second optical circulator 509B directs the first reflected light beam to a second focussing optic 51 1 B.
  • the focussing optic 51 1 B includes two lenses that are used to focus the input signal 507 onto elements 513x (i.e. 513A, 513B etc.) of the phase plate 515.
  • the focussing optic 51 1 B also receives a second reflected light beam reflected off an element of the phase plate. This second reflected beam, is directed by the second optical circulator 509B along optical path 519A as an output beam 515 towards the optical measurement system.
  • further cascading optical delay lines may be incorporated where the second reflected beam, is directed by the second optical circulator 509B along optical path 519B to a further optical circulator within the further cascading optical delay line.
  • the optical signal coming from an optical delay element is a version of the optical signal directed towards that optical element after it has acquired a time-dependent optical delay introduced by the optical delay element.
  • the elements towards or onto which the input light signal and reflected beam(s) may be directed may be the same element or different elements. That is, the initial light beam from the first optical delay line 503A may be directed towards a first element 513A of the phase plate 515, and a reflected light beam from the second optical delay line 503B may be directed towards the same first element 513A.
  • the location of the beams on the element would be different, but may be at the same radial angle on the phase plate but at a different radial distance from the centre of the plate.
  • the location of the beams may be at different radial angles on the phase plate, but at the same radial distance from the centre of the plate.
  • the focussing optic enables the light beam to be directed towards a desired element of the phase plate and a desired position on that element, and so could include a mirror, lens, multiple lenses, multiple mirrors or any combination thereof.
  • the positional control of the focussing optics for directing each light beam onto the element(s) of the phase plate may be a manual process
  • a computing device (as described with reference to Fig 1A and 1 B) may be used as a control system to control the positioning of the focussing optics.
  • the computing device may provide a user interface to enable a user to input or control a variable that is output from the computing device to control a positioning device connected to the focussing optics.
  • a position controller may be one or more of: a motor (or other positional actuator) to move the position, direction or orientation of the optical circulator to change the direction of the optical beam(s), a motor (or other positional actuator) to move the position, direction or orientation of the focussing optics to change the focus and/or direction of the optical beam(s), a beam steering device to change the position, focus and/or direction of the optical beam(s), or any other suitable position controller for controlling the direction, position or focus of the optical beam(s).
  • the position controller is arranged to control the position of the optical delay elements relative to the optical beam (or signal).
  • a step motor may be controlled by the computing device to move the position of the focussing optics in order to direct the beam of light associated with each focussing optic.
  • the control system may be used to control the speed of rotation of the motor that is used to rotate the phase plate.
  • a feedback system may be employed where the current scan rate and scan depth are fed back to the control system, and the control system determines whether adjustments are required based on the desired scan rate and scan depth.
  • synchronous and asynchronous positioning of the light beams may be controlled by the computing control system dependent on the desired scan rate and scan depth.
  • the second light beam is a reflected version of the first light beam (input beam) and a third light beam (output 515) is a reflected version of the second light beam. That is, the second light beam (optical signal) is a version of the first light beam (optical signal) that has acquired a first time-dependent optical delay introduced by the first element of the rotating phase plate 515. As the light beam is cascaded through further optical delay lines, the beam acquires further time-dependent optical delays based on the elements of the rotating phase plate.
  • the collimated output 517A of the first optical delay line 503A is focused onto the first segmented (or ramped) surface of an element 513A of the rotating phase plate 515.
  • the returning beam 503B is then re-directed to the second optical delay line 503B and onto the second segmented (or ramped) surface of an element 513C of the rotating phase plate 515.
  • the approximate position on the phase plate 515 of the two light beams (517A, 517B) is indicated by dots 517A and 517B in Figure 5A.
  • the position of the two beams (517A and 517B) produces a synchronous output as explained in more detail herein.
  • the phase plate in Fig 5A is shown to have 69 segments around the circumference of the phase plate.
  • the maximum height of an individual segment or element h 200 ⁇ , and the elements have a ramp profile with a smooth surface.
  • Fig 5A also shows the position of two beams (517A and 517C) that produces an asynchronous output as explained in more detail herein.
  • Figure 5B shows an example of the optical delay line system with a cascading fibre- based reflection system integrated into a time-domain optical coherence tomography system. The round trip of the incident and returning beams is circled back using a 50/50 fibre splitter.
  • the time domain OCT system 551 shown in Figure 5B has an SLED 553 that generates light of wavelength 1310 ⁇ 85 nm that is launched into a first 90/10 fibre splitter 555, where 10% is projected onto the side of the rotating phase plate and retro reflected onto a photodiode (PD) 556 to provide a timing pulse for synchronising each rotation, where the timing pulse 558 is fed back to the data acquisition system 1301.
  • the remaining 90% of the light is directed to a beam splitter 557, where the beam is directed towards a second 90/10 splitter 559.
  • the second 90/10 splitter 559 outputs 10% of the signal to a reference arm 561 and the other 90% to a sample arm 563 of an optical system.
  • the OCT system analyses the optical length of the two arms (sample and reference) in to obtain relevant measurements of the sample.
  • the system is initially setup so that the sample and reference arms have the same optical length (or delay).
  • the sample can be analysed.
  • a 50:50 beam splitter 565 is used to launch an initial beam 507 into the optical delay line system 501 and onto a first element (segmented surface) of the phase plate (see Figure 5a).
  • An output beam 515 re-enters the 50:50 splitter 565 and combines with a sample signal 569 obtained from the imaging system sample arm in the 90:10 splitter 559.
  • the eventual interference signal is then detected by the balanced photodiode and measured by the data acquisition/computing system 1301 .
  • a two-axis galvo mirror 571 is positioned to provide raster scanning for tomographic imaging.
  • the signal is then digitised and filtered using data acquisition/computing system 301 for real-time processing.
  • the rotating phase plate used here comprises of 69 mirror segments (elements). At a rotation rate of 300 Hz this gives a basic scan rate of 20.7 kHz, and a scan depth of 200 ⁇ (based on the physical height of all the elements of the phase plate on which the beam is directed). Under the synchronous positioning, the scan depth should also double and under asynchronous the scan rate should also double.
  • the timing of the optical delay system can be adjusted without further extension of the overall path length of the optical delay system.
  • Figures 6a-6f show the performance of a system using cascading optical delay lines with a segmented phase plate in terms of duty cycle and single depth scan (i.e. single beam pass) respectively.
  • Figures 6a, 6b and 6c show the results of an asynchronous method
  • Figures 6d, 6e and 6f show the results of the synchronous method.
  • the duty cycle is based on the back reflected signal (output of the delay line system) by measuring the time during which a non-zero reflected signal is detected with respect to the time required to complete one scan of a segment (or half segment if in asynchronous mode). The duty cycle is effectively a
  • Figures 6a - 6f show experimental data of the reflected power and interference signals when the beams are asynchronous (6a, 6b, 6c) and synchronously matched (6d, 6e, 6f) respectively.
  • the reflected power measurement shows a repetition rate of 42.7 kHz that corresponds to readout of interference fringes in Fig 6c.
  • repetition rate is maintained at 20.5 kHz (Fig. 6e) that corresponds to the interference fringes in Fig. 6F.
  • the repetition rate is maintained at 42.7 kHz (Fig 6B) that correspond to the interference fringes shown in Fig 6C.
  • FIGS. 6A and 6D correspond to the asynchronous mode and synchronous mode of operation respectively.
  • Fig 6A is representative of the signals generated in accordance with the optical beams generated according to the method described with reference to Fig 4C.
  • Fig 6D is representative of the signals generated in accordance with the optical beams generated according to the method described with reference to Fig 4B.
  • Figures 6A and 6D show the relationship between the initial optical signals and reflected optical signals for each of the synchronous and asynchronous modes of operation.
  • the first pass (initial signal delay line), second pass (second delay line which uses the reflected signal from the first delay line as input) and sum of the two signals are shown.
  • Figures 7a and 7b show video rate OCT imaging signal at 600 Hz with asynchronous beam positioning on a vibrating reflective film at 40 Hz.
  • Fig 7a shows each B-scan of the sample over 200 ⁇ depth and
  • Fig 7b shows a plot of the full oscillatory motion over multiple cycles.
  • the achievable frame rate is equivalent to 600 fps per B-scan, thus capturing millisecond dynamic of the vibrating film
  • FIG. 8a shows the double depth image (as illustrated in Figure. 4b) where the synchronous position of the beam achieves twice the scan depth (400 ⁇ ).
  • Figure 8b shows an example showing extended scan depth
  • FIG. 8c shows the 3D reconstructed image of the leaf produced by the synchronous method.
  • Figure 8d shows an image of the venation structure in the leaf that is present specifically at around 300 ⁇ in depth, taken from the volumetric data of Figure 8c, and thus also produced by the synchronous method.
  • the herein described system provides flexibility and simplicity to switch between deeper imaging depth and faster imaging.
  • a time-domain OCT system is provided that operates at video rates at > 40 kHz (depth scan) that potentially achieves (600 x 68) lines per second.
  • this technique has the capability to scale up by increasing the number of phase plate segments the beam is applied to by cascading further optical delay lines, wherein the physical space between each fibre in the delay lines is sufficiently spaced to ensure good coupling.
  • the system has a scan rate of 20 and 40 kHz.
  • the rotating phase plate is spun with a low torque motor ( ⁇ 300Hz) inside a reference arm of a time domain OCT.
  • the new video rate time-domain optical coherence tomography imaging system achieves imaging speeds of up to 600 fps - B scan and is capable of capturing a fast vibrating film (40 Hz).
  • FIG. 2 is a process flow diagram of a method for controlling an optical signal in an optical delay line system.
  • a first optical signal is received from an optical system.
  • the first optical signal is directed to a first optical delay element (such as an element on a phase plate).
  • a second optical signal is received, where the second optical signal is a time-dependent optically delayed version of the first optical signal.
  • the second optical signal is directed to a second optical delay element.
  • a third optical signal is received, where the third optical signal is a time-dependent optically delayed version of the second optical signal.
  • the third optical signal is directed towards either a further optical delay element or the optical system.
  • any suitable component(s), including optical fibres, mirrors, lenses, circulators and other optical components, may be used to control the optical beam direction or routing to, from and/or within one or more optical delay lines.
  • any suitable phase plate configuration may be used where at least two beams can be reflected from or transmitted through one or more elements of the phase plate such that the beam position may be adjusted between i) a first synchronous mode where the depth (i.e. height of the element) of the initial beam and reflected beam is the same, and ii) a second asynchronous mode where the depth (i.e. height of the element) of the initial beam and depth of the reflected beam is different.
  • the rotating phase plate may have a single step rotating that goes from a minimum to a maximum height around the entire circumference of the plate. By positioning the beams accordingly, the initial beam and reflected or transmitted beam may be at the same height or different heights. As a further alternative, there may be two or more steps (elements) around the circumference of the phase plate.
  • a first cascading delay line 1001 includes an optical fibre 901 , optical focussing devices 903A and 903B, and optical focussing devices 909A and 909B.
  • the first cascading delay line 1001 receives an optical signal from an optical system (such as an OCT system) via an optical fibre 901 (or other suitable beam routing mechanism).
  • the optical signal is provided to the optical focussing devices (903A, 903B) to direct (or focus) the optical beam towards the rotating phase plate 905.
  • the rotating phase plate 905 in this example has multiple optical delay elements (907A, 907B, 907C) formed from a transparent or semi-transparent material, such as glass or any suitable polymer material.
  • the difference between the refractive index of the optical delay element material and the surrounding medium (e.g. air) causes the change in path length, phase change or optical delay.
  • the optical signal coming from the optical delay element is a version of the optical signal directed towards the optical element that has acquired a time-dependent optical delay introduced by the optical delay element.
  • the optical signal received through the input beam routing device (901 ), e.g. fibre, is not reflected back to the optical focussing devices (903A, 903B) but is transmitted through the optical delay element 907A of the phase plate 905 to the optical focussing devices (909A, 909B).
  • the optical focussing devices (909A, 909B) combined with an optical beam routing device (91 1 ) direct the optical signal to the next cascading delay line 1003.
  • This next cascading delay line 1003 includes optical focussing devices (913A, 913B), optical fibre (91 1 ) and optical focussing devices (915A, 915B).
  • the same process as described with reference to the first cascading delay line occurs using the optical fibre 91 1 (or other suitable optical routing device), optical focussing devices (913A, 913B), optical delay element 907B of the phase plate 905 and optical focussing devices (915A, 915B).
  • the optical fibre 917A directs the optical signal either back to the optical system, or towards a further cascading delay line 1005 via fibre 917B.
  • the further cascading delay line includes optical focussing devices (919A, 919B), optical focussing devices (921A, 921 B) and optical fibre 923.
  • the optical signal received at the third cascading delay line is directed towards optical delay element 907C of the rotating phase plate 905.
  • optical delay element(s) may be formed on or from devices other than rotating phase plates.
  • a series of optical delays may be provided by two optical fibres that are stretched and which are at a constant offset to one another, where the optical beam is passed through the optical fibres multiple times.
  • a linear configuration of optical delay elements in the form of ramps may be used where the optical delay elements are moved in such a fashion that the delayed beams change their respective delays synchronously and where the herein described technique is used to cascade the individual delays in either a synchronous or asynchronous fashion. Therefore, the multiple optical delay elements provide a general time dependent optical delay with multiple individual points that can be accessed independently and that are inherently at a constant relative scan position.
  • FIG. 10A One example of an alternative mechanism for moving the optical delay element(s) relative to the optical beam(s) is shown in Fig. 10A where a first optical delay line 101 OA has a first optical signal routing device 1012A, which in this example is an optical circulator.
  • the optical signal is fed from the first optical signal routing device 1012A to a first optical signal focussing device 1014A.
  • the first optical signal focussing device 1014A directs the optical signal towards a first optical delay element 1016A that is formed on, attached to or otherwise engaged with an optical delay element transport mechanism 1018.
  • the transport mechanism 1018 may be any suitable platform upon which the optical elements are placed or positioned.
  • the transport mechanism 1018 is arranged to move up and down in a reciprocal manner through interaction with a position controller (not shown), such as a step motor for example.
  • a position controller such as a step motor for example.
  • the optical delay elements are reflective and reflect the optical beam back to the first optical delay line 101 OA in a similar manner to that shown and described with reference to Fig 5A.
  • Additional optical delay lines (1010B, 1010C, 1010D, 1010E etc.) are provided to cascade the optical signal through multiple optical signal routing devices (1012B, 1012C, 1012D, 1012E etc.) and multiple optical signal focussing devices (1014B, 1014C, 1014D, 1014E etc.) where the outputs and inputs of the multiple optical signal focussing devices (1014B, 1014C, 1014D, 1014E etc.) direct the optical signal to and receive the optical signal from multiple optical delay elements (1016B, 1016C, 1016D, 1016E etc.).
  • FIG. 10B A further example of an alternative mechanism for moving the optical delay element(s) relative to the optical beam(s) is shown in Fig. 10B where the same optical delay lines (101 OA - 1010E etc.) are used.
  • the optical signal is directed towards a optical delay elements (1018A, 1018B, 1018C, 1018D, 1018E etc.) that are formed on, attached to or otherwise engaged with an optical delay element transport mechanism (1020, 1022).
  • the optical delay elements (1018A, 1018B, 1018C, 1018D, 1018E etc.) are formed on, attached to or otherwise engaged with a belt 1020, which is positionally controlled by way of, for example, a motor connected to one or more rotating elements (1022A, 1022B).
  • the transport mechanism (1020, 1022) is arranged to move up and down in a reciprocal manner through interaction with a position controller (not shown), such as a step motor for example.
  • the transport mechanism (1020, 1022) may be arranged to move the belt in one direction in a repeating loop through interaction with a position controller (not shown), such as a motor for example.
  • the mirror may be controlled by the position controller to move (reciprocate) the mirror up and down.
  • the optical delay system could only operate in a synchronous mode.
  • optical delay lines described herein may be used in many optical applications including optical communications, optical ranging, laser imaging and optical coherence tomography.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Theoretical Computer Science (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)

Abstract

La présente invention concerne un système de ligne à retard optique comprenant : une pluralité de lignes à retard en cascade adaptées pour utilisation dans un système optique, une première ligne à retard en cascade d'au moins deux de la pluralité de lignes à retard en cascade étant agencée pour : diriger le premier signal optique vers un premier élément de retard optique ; et recevoir un deuxième signal optique, le deuxième signal optique étant une version du premier signal optique qui a acquis un premier retard optique dépendant du temps introduit par le premier élément de retard optique ; une deuxième ligne à retard en cascade d'au moins deux de la pluralité de lignes à retard en cascade étant agencée pour : diriger le deuxième signal optique vers un deuxième élément de retard optique ; et recevoir un troisième signal optique, le troisième signal optique étant une version du deuxième signal optique qui a acquis un deuxième retard optique dépendant du temps introduit par le deuxième élément de retard optique, et diriger le troisième signal optique soit vers une autre ligne à retard en cascade de la pluralité de lignes à retard en cascade, soit vers le système optique.
PCT/AU2017/000121 2016-06-01 2017-05-31 Améliorations de lignes à retard optique Ceased WO2017205892A1 (fr)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7433046B2 (en) * 2004-09-03 2008-10-07 Carl Ziess Meditec, Inc. Patterned spinning disk based optical phase shifter for spectral domain optical coherence tomography
US20140078510A1 (en) * 2011-05-20 2014-03-20 Medlumics S.L Scanning device for low coherence interferometry

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7433046B2 (en) * 2004-09-03 2008-10-07 Carl Ziess Meditec, Inc. Patterned spinning disk based optical phase shifter for spectral domain optical coherence tomography
US20140078510A1 (en) * 2011-05-20 2014-03-20 Medlumics S.L Scanning device for low coherence interferometry

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHEN, N.G. ET AL.: "Rotary mirror array for high-speed optical coherence tomography", OPTICS LETTERS, vol. 27, no. 8, 2002, pages 607 - 609, XP001115264 *

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