TW201812383A - Spatial chirped cavity for temporally stretching/compressing optical pulses - Google Patents

Abstract

Systems and methods tor optical pulse stretching or compression in time are provided. An apparatus of the subject invention can operate as an optical dispersive element for optical pulse stretching or compression in time, as well as laser scanning in space. An apparatus can include a spatial disperser arranged to divide a collimated optical pulsed beam into a beamlet array of beamlets with equally spaced angles, a beam shaper configured to control the spreading angle of the beamlet array, and a cavity to sequentially reflect the individual beamlets within the beamlet array. The cavity can include two non-parallel surfaces, such as two non-parallel mirrors.

Description

 Space cavity for stretching/compressing optical pulses over time  

The present invention relates to a spatial cavity for stretching/compressing optical pulses over time.

Pulse stretching and compression are useful in many applications. One of the most common techniques for achieving effective pulse stretching/compression is the use of long dispersion fibers in which light pulses are directed and propagated. A key attribute for accomplishing this task using fiber optics is the dispersion of an optical fiber (typically quartz glass) in which different frequency components are subjected to different refractive indices and propagate efficiently along the fiber at different rates. It therefore separates the different frequency components within the pulse in time, ie the pulse stretching. The dispersing element can also be used as a compressor for optical pulses, wherein the time-expanded light pulses can be recompressed into pulses that meet the desired application. For example, this operation can be performed to avoid excessive time stretching of ultrashort pulses, which can cause distortion of signals in telecommunications and in optical microscopy/imaging.

While optical fibers have been well recognized as one of the most conventional dispersive components (for pulse stretching/compression), they have limitations that hinder the use of fiber optics in a wider range of applications. The pulsed stretch/compressible allowable operating wavelength range is limited by the material of the fiber (more specifically, optical loss). Since ordinary fibers are made of quartz glass, optical loss and hence effective pulse stretching/compression are optimized to near-infrared spectral windows from 1 μm to 1.5 μm. This means that the wavelength of the optical pulse on which the optical stretching/compression can be performed strongly depends on the material loss of the fiber, ultimately limiting the operating range of the wavelength.

Furthermore, in fiber optics, pulse stretching/compression cannot be active or dynamically tunable. The amount of pulse stretching/compression using the fiber is controlled by the dispersion experienced by the optical pulse. The total dispersion is directly proportional to the length of the fiber, and in general, once the fiber has been fabricated, the length of the fiber is fixed and not flexible (and widely) adjustable.

In addition, the group delay dispersion (GDD) accumulated by optical pulses in the fiber is limited, and the amount of time stretching also depends on the optical bandwidth of the pulse. Therefore, long fibers (approximately tens of kilometers of standard telecommunications fibers) are needed in order to obtain sufficient GDD for efficient pulse stretching/compression. From a design perspective, the use of optical fibers for pulse stretching/compression is spatially inefficient.

In addition, the optical nonlinearity associated with all materials in existing devices is unavoidable and detrimental to pulse stretching/compression. Particularly in optical fibers, optical pulses are not only subjected to linear dispersion (i.e., a constant refractive index at each frequency), but also to nonlinear effects in which the refractive index depends on the power distribution of the optical pulse envelope. The optical pulses and thus the encoded information are eventually distorted during the stretching/compression process.

On the other hand, pulse stretching has been used together with techniques for performing spatiotemporal mapping to achieve optical beam scanning or manipulation. This approach allows for optical beam scanning where mechanical moving parts such as scanning mirrors are required, and thus bypasses basic speed limits (limited by inertia) and motion artifacts of such mechanical based beam scanners. Laser beam scanning applications have been extensively involved in bar code scanning, biomedical imaging, materials science, laser beam processing and ablation, and automated surface inspection in manufacturing (including semiconductor integrated circuits in the ultra-large scale integration (VLSI) industry). (IC) wafer fabrication). In these applications, optical beam scanning is performed by spatially deflecting the beam using optical elements. Common choices include galvanometer mirrors and acoustic optical deflectors.

In general, beam scanning can be classified into active or passive scanning, depending on the feasible implementation. Active beam scanners require controllable elements to alternate (or manipulate) the direction of the optical beam. For example, in laser scanning imaging/spectroscopy (widely used in life sciences or materials science applications), it is possible to continuously manipulate the laser beam from a galvanometer mirror over a range of angles. By combining with an appropriate relay lens system, such angular beam displacements can be transformed into lateral beam displacements to enable lateral scanning of the focused beam across the sample under test (eg, biological cells/tissue). The spatial information of the sample (due to absorption, scattering or luminescence) is read out in time by the scanned beam. Therefore, the single-pixel photodetector can be used to retrieve the bull's-eye chart image from the serial time signal. Ultimately, the scanning rate of these techniques is substantially limited by the speed of the moving deflection optics and the mechanical movement of these devices. Galvanometer mirrors are widely used in most commercial laser scanning systems; however, due to mechanical inertia in all galvanometer mirrors, including microelectromechanical systems (MEMS) scanners, it can only provide one up to 500 Hz or 1 kHz. Dimensional (1D) line scan rate, by operating the mirror at the resonant frequency of the mirror (ie, a resonant galvanometer mirror) - most up to about 10 kHz, enables a modest improvement in scan rate. To overcome mechanical limitations, acoustical optics (AO) and electro-optical (EO) modulators have been invented to achieve higher scan rates of approximately sub-MHz to MHz. However, the use of these devices achieves high scanning speeds at the expense of a smaller range of scan angles and smaller resolvable scan points (i.e., field of view). AO devices also suffer from additional optical losses due to the diffraction effects of the device, while EO devices typically require high voltages (>100 V) to achieve a reasonable scan range for viable imaging applications.

Unlike active beam scanning, passive beam scanning is a technique that does not involve direct manipulation of beam steering/scanning. A notable example is beam scanning based on spectral coding mechanisms. In this technique, a wavelength tunable light source (referred to as a sweep source) having a broadband wavelength spectrum is employed. The output light wavelength is swept in time. Thus, by using optical elements called spatial dispersers (eg, prisms, diffraction gratings, virtual imaging phase arrays, etc.), it is possible to map beams at different wavelengths to different spatial coordinates on the sample being tested (can be one-dimensional or Two-dimensional). Since the wavelength is swept in time, it is basically possible to scan the beam across the sample. Beam steering is thus indirectly achieved by wavelength tuning and spectral coding concepts (ie, wavelength space mapping). The beam scanning speed of this technique is primarily determined by the wavelength sweep rate of the laser, which is generally limited to 1 kHz or 100 kHz in current state of the art.

A conventional dispersion medium used in optical time stretching techniques is an optical fiber. To achieve high resolution beam scanning, a large amount of dispersion (i.e., pulse stretching) is required. This requires a long length of fiber (greater than 10 kilometers), which inevitably results in amazing optical losses. The low loss spectral region of a typical optical (glass) fiber is from about 1 [mu]m to about 1.5 [mu]m, limiting the operating wavelength range and thus limiting the application of this technique.

Embodiments of the present invention provide advantageous systems and methods for stretching or compressing optical pulses over time and thus performing optical beam scanning spatially. The apparatus of the present invention is capable of operating as an optical pulsed optical dispersion element and an optical spatial beam scanner for stretching or compressing in time.

In an embodiment, an apparatus for stretching and/or compressing optical pulses can include: a spatial disperser arranged to split a collimated optical pulse beam into sub-beam arrays of sub-beams of equal spacing, configured to control A beamformer of the extended angle of the sub-beam array and a cavity of the individual sub-beams within the sub-beam array are sequentially reflected. The cavity can be a spatial cavity and can, for example, comprise two non-parallel reflective inner surfaces (eg, mirrors). The separately reflected sub-beams can each be encoded with different time information in sequence, and can be used as an optical spatial scanning beam without involving any mechanical moving parts.

1‧‧‧Light input

2‧‧‧Space diffuser

3‧‧‧beamformer

4‧‧‧啁啾 cavity

5‧‧‧ Output

12‧‧‧Diffraction grating

13‧‧‧ lens

14‧‧‧ cylindrical lens

15‧‧‧Repeating mirror

16‧‧‧Mirror

17‧‧‧Mirror

18‧‧‧Mirror

19‧‧‧Mirror

20‧‧‧啁啾 spiral track

21‧‧‧啁啾Spiral track

22‧‧‧ Octagonal cavity

22A‧‧‧Light trajectory

23‧‧‧Relay optical system

24‧‧‧Scanning beam

25‧‧‧Type I Space Diffuser

26‧‧‧beam splitter

27‧‧‧Photodetector

28‧‧‧Type II Space Diffuser

29‧‧‧Dichroic Mirror

Figure 1 shows a schematic representation of the apparatus of the present invention.

Figure 2 shows a cavity according to an embodiment of the invention.

Figure 3 shows a schematic of a colored stretch/compress optical pulse.

Figure 4 shows a graph of the input and output spectra of an optical pulse.

Figure 5A shows a graph of a time stretched optical signal stretched by a dispersed fiber.

Figure 5B shows a graph of a time stretched optical signal stretched by an embodiment of the present invention.

Figure 6 shows a schematic diagram of pulse stretching based on a second type (Type II) of spatial diffusers (e.g., lenses) used.

Figure 7(a) shows a plot of group delay dispersion as a function of mirror pair separation.

Figure 7(b) shows a plot of group delay dispersion as a function of mirror pair separation.

Figure 8A shows a single input optical pulse.

Figure 8B shows a pulse train generated by an embodiment of the present invention.

Figure 9 shows a schematic diagram of an apparatus according to an embodiment of the invention based on a first type (Type I) of spatial diffusers used.

Figure 10A shows a top schematic view of a spatial cavity (in a square cavity, side length (N) = 4), in accordance with an embodiment of the present invention.

Figure 10B shows a side view and a two-pass optical trajectory of a spatial cavity (in a square cavity, N = 4), in accordance with an embodiment of the present invention.

Figure 10C shows a top schematic view of a spatial cavity (in the octagonal cavity, N = 8), in accordance with an embodiment of the present invention.

Figure 11 shows a schematic of the apparatus of the present invention for laser beam scanning.

Figure 12A shows a schematic of the apparatus of the present invention for laser beam scanning based on the type I spatial disperser used.

Figure 12B shows a schematic of the apparatus of the present invention for laser beam scanning based on the type II spatial disperser used.

Figure 12C shows a schematic of the apparatus of the present invention for laser scanning fluorescence imaging based on a type II spatial disperser used.

Figure 13A shows a bright field laser scanned image of a resolved target captured by the apparatus of the present invention based on the Type II spatial diffuser used.

Figure 13B shows a bright field laser scanned image of a lung tissue section captured by the device of the present invention based on the type II spatial disperser used.

Embodiments of the present invention provide advantageous systems and methods for stretching or compressing optical pulses over time. Due to the ordered spatiotemporal mapping provided by the apparatus of the present invention, the apparatus is capable of operating as an optically dispersing element for stretching or compressing optical pulses and/or performing spatial beam scanning over time.

Optical pulse stretching and compression are useful for a wide range of applications, including optical imaging/microscopy in biomedical applications, fiber optic or free-space optical data transmission in telecommunications, and remote sensing in industrial and military applications. For example, to overcome detection bandwidth limitations (especially when high-speed photodetectors are not readily available in optical wavelengths of interest such as the mid-infrared range, etc.), a series of short optical pulses can be stretched over time prior to detection, each The pulses carry bit (1 and 0) information (ie, the information can be "decelerated").

In a spectroscopy environment, all components in an optical broadband pulse encoded with microscopic information (eg, from molecules or biological cells/tissues) can be limited in time and in ultra-short-time windows (eg, sub-picoseconds) Overlap to Yana seconds). Pulse stretching is capable of sequentially separating frequency components in time and can therefore be used to analyze spectral features intrinsically without the use of a conventional spectrometer. This is particularly relevant when no effective spectrometer is available in the wavelength of interest, or when ultrafast spectral analysis is required.

Embodiments of the present invention can advantageously bypass the use of optical fibers and common diffraction by providing a new concept for performing pulse stretching and/or compression in an unprecedented wide wavelength spectrum for achieving highly scalable and flexible tuning of dispersion. The component performs time pulse stretching and compression. The wavelength spectrum in which the embodiment of the present invention can perform pulse stretching and/or compression can be, for example, from ultraviolet light to infrared light (for example, including all wavelengths in these frequency bands), but the embodiment is not limited thereto. The dispersion (e.g., group display dispersion (GDD)) provided by the apparatus and method of the present invention can be superior to the prior art. The present invention is capable of using an air cavity filled with air to provide a scalable delay of different frequency components, and an optical cavity filled with air can be referred to as a spatial cavity or cavity. In many embodiments, the spatial cavity can include a pair of mirrors, and the mirrors can be non-parallel to each other. In a particular embodiment, the spatial cavity can be comprised of a pair of non-parallel mirrors and air.

In many embodiments, the scalable delay of the different frequency components can rely on the use of an optical cavity filled with air (or free space), which cavity can be referred to as a spatial cavity or cavity. The space cavity can include a pair of mirrors, and the mirrors can be non-parallel to each other. This enables the use of highly scalable optical delays in the air path. Therefore, the dependence on the dispersion of any material can be completely eliminated. Embodiments can be extended to any wavelength region without suffering any material loss, such as from ultraviolet to infrared wavelengths, but embodiments are not limited thereto. Previously, a wide range has not been achieved by the related technology pulse stretching/compression technology.

The present invention provides a flexible way of adjusting the amount of GDD by simply adjusting the spacing between the mirrors of the cavity. In addition, the design is capable of dynamically selecting normal or abnormally dispersed regions, a unique feature that does not exist (or at least hardly exists) in fiber-based pulse stretching/compression techniques. Embodiments of the present invention can provide a dispersion amount that is more than an order of magnitude greater than the amount of dispersion of a related free space time stretching/compression device, such as a prism pair or a diffraction grating pair. In addition, the range of tunable GDDs is highly scalable (eg, between femtoseconds and nanoseconds), while the footprint of the device remains small and compact.

Figure 1 shows a schematic representation of the apparatus of the present invention. Referring to Figure 1, optical input 1 (or referred to as source 1) can pass through spatial diffuser 2 (or spatial beam spreader 2), and spatial diffuser 2 can distribute the spectral (frequency) components of the beam to In space. The input 1 can, for example, come directly from a light source free space that is output or coupled from a light guide such as an optical fiber, but the embodiment is not limited thereto. The spatial diffuser 2 can be any type of diffractive optical element, such as a diffraction grating or a dispersion prism, or any type of beam diverging element, such as a lens, but embodiments are not limited thereto. The spatially scattered optical beam can then optionally be reshaped by beamformer 3 (eg, a beam expander or compressor based on a compound lens system) and can be coupled to a cavity 4 filled with air (or called Space cavity 4). The cavity 4 can include a pair of non-parallel mirrors and air (ie, a Fabry-Perot-like cavity). The optical path difference between the frequency components (ie, GDD) can be neglected before entering the cavity. The spectral components can then be reflected back by the cavity 4 and their optical paths can be reversed. All reflected spectral components can be recombined in the spatial diffuser 2 and output 5 just after the spatial diffuser 2.

After passing through the spatial diffuser 2, and optionally through the beamformer 3, different frequency components of the optical beam can enter the cavity at different angles of incidence. They can thus be constrained in the cavity with different "tortuous" trajectories, as shown in Figure 2, which can create optical path length differences between the frequency components of the light. However, this mechanism itself does not guarantee a highly scalable GDD. Figure 2 shows a schematic view of the sacral cavity. Referring to Figure 2, the advantageous features of the non-parallel mirror configuration 6 of the bore cavity can result in a meandering trajectory. That is to say, when the light propagates in the cavity, the tortuous path can become more compactly squeezed together. In other words, the angle of incidence of each reflection in the two mirrors can be gradually reduced until it reaches zero (ie, normal incidence). Due to the different input coupling angles into the cavity, individual frequency components can propagate different path lengths until they reach their respective normal incidence positions in the cavity. Therefore, the 啁啾 trajectory can greatly enhance the path length difference. In addition, GDD can be dynamically tuned over a wide range by simply adjusting the separation of the mirrors of the cavity R 8 . In addition, by changing the input beam orientation, GDD can flexibly exchange between anomalies and normal dispersion areas. This can be done, for example, by using a beamformer or simply mechanically redirecting the cavity. These effective GDD tuning features are not present (or at least barely present) in all types of fibers.

Figure 3 shows a schematic of a colored stretch/compress optical pulse. Another unique feature of embodiments of the present invention is that the tortuous trajectory can be reversible such that the optical beam can not only recover its original input beam profile, but its GDD can be doubled by a two-pass meandering trajectory, as in Figures 2 and 3. Shown. Restoring the input beam profile (i.e., maintaining high optical beam quality) is of great importance in its compatibility with many applications. For example, high optical beam quality should be maintained: when the device is used as an ultrafast wavelength sweep source; when the beam is to be coupled into an optical waveguide (such as an optical fiber) to ensure high coupling efficiency; and the beam needs to be effectively relayed to the system When other optical components are in use.

Referring again to Figure 3, the diffraction grating 12 can be used as a spatial disperser. The groove density of the grating can be selected according to the target spectral resolution and the operating wavelength region. The spatially dispersed beam can be relayed by a beamformer 3, which can be a 2-lens 13 telescope system in a 4F correlator configuration such that the diverging beams can be concentrated before being coupled to the cavity 4. The focal lengths of the two lenses can be the same or different. The combination of the two lenses can effectively modify the convergence angle of the sub-beam array and thus modify the meandering trajectory of the frequency components in the cavity. Referring to Figure 9, in some embodiments, a looper and fiber collimator can be used together prior to the diffraction grating.

As shown in Figures 2 and 3, the concentrating sub-beam array (spatial scattered beam) can be mixed at the mirror behind the cavity input (labeled fulcrum 7). Each frequency component can then be constrained in the cavity with its unique meandering path, bounce back and forth between the front and rear mirrors. Once the angle of incidence on either of the two mirrors reaches zero (ie, normal incidence), the beam is then reflected back, reversing the direction of propagation along the same optical path. The beam that is eventually stretched or compressed in time recovers its original input beam profile. This output beam can be extracted by an optical looper or an optical splitter (both of which can be free-space or fiber-based components).

To achieve this, two conditions must be met. First, the front mirror is tilted at an angle A/m 10 relative to the rear mirror, where m is an integer. This tilt angle exactly matches the multiple division of the minimum resolvable angle A 9 of the spatially dispersed sub-beam array determined by the parameters of the diffraction grating. Based on direct geometric ray tracing, it can be understood that after each reflection from the front or back mirror, the angle of incidence of each frequency component relative to the next mirror will be reduced by A/m. This reduction is linear and proportional to the angle of inclination A/m between the two mirrors and the number of bounces. Second, the input incident angle of the innermost frequency component (eg, the red beam as shown in Figures 2 and 3) must be an integer multiple of the mirror tilt angle, i.e., nA/m 11, where n is another integer.

In general, the amount of GDD of an optical pulse is determined by four quantities associated with the mirror pair: the spatial separation of the mirror pairs - R 8 ; the inclination of the mirror pair - A / m 10; the angle of incidence of the frequency comb - nA / m 11; The incident orientation of the frequency comb (for normal or abnormal dispersion).

More specifically, GDD can be expressed as a function of the optical frequency ω:

Where R 8 is the mirror-pair separation, k is the order of each bounce for the individual beams, and N(ω) is the total number of bounces along the meandering path for the individual beams (associated with different frequencies ω). It is provided by the incident input angle relative to the bore and the total angular spread of the input convergence sub-beam array. Similarly, A is the angular separation between the two smallest resolvable frequency components of the spatially dispersed beam before entering the cavity, and is determined by the focal lengths f ₁ and f _{2 of the}刻 and 4F systems during grating grooving, And stated as

Where ω is the central angular frequency of the ray and c is the speed of light.

Multiple parameters (e.g., grating groove density, ray comb incidence angle, lens focal length) can be tuned to adjust the amount of GDD in the device of the present invention. For illustrative purposes only, the highly scalable GDD tunability provided with variations in the separation of the mirror mirror R is demonstrated. Figures 7(a) and 7(b) show graphs of GDD as a function of mirror pair separation. Referring to Figure 7(a), the GDD is directly proportional to the mirror space separation R. Figure 7(b) is an enlarged version of the pattern of Figure 7(a) in a small GDD region, where the amount of GDD is similar to the tunability of a technique free space pulse stretching/compression device (e.g., grating pair or prism pair pulse) The stretcher/compressor), while the large GDD area is not achievable by the related art pulse stretching/compression device. In order to achieve a large GDD, the size of the cavity can be set, for example, to R=5 cm, and the mirror length is 17 cm, but the embodiment is not limited thereto; and for small GDD, the size of the cavity can be reduced to, for example, R=1 mm, And the mirror length is 4 mm, but the embodiment is not limited thereto. The apparatus of the present invention is much more compact and more compact than typical fiber lengths that can provide the same large amount of GDD as the apparatus of the present invention (typically using fiber-optic reels, about 10-100 kilometers). The size can even fit into the shoe box.

In many embodiments, pulse stretching can be the result of input angle dependent delay differences. Therefore, the sub-beams of the input light to the cavity do not necessarily have a wavelength dependent input angle. In other words, even with narrow-band long pulses (eg, picoseconds), many pulse stretches are possible without having to resort to most picoseconds that require specialized control to achieve a stable firing to the firing operation or SC source.

Spatial diffusers used in embodiments of the present invention can have two main types: Type I refers to spectrally encoded components (e.g., prisms or diffraction gratings), and Type II refers to angularly encoded components (e.g., lenses or Fresnel strips). These two types of dispersers disperse the optical beam or cause the optical beam to diverge by two different operating principles.

A Type I spatial disperser basically performs spectral encoding in which the wavelength components of the source are mapped to different angular propagation directions (ie, the beam is transformed into an array of spectrally encoded "sub-beams"). As discussed herein, the GDD or generally the path length difference between different spectral components caused by the spatial chirp is highly dependent on the sub-beam angle. Thus, the spatial cavity provides substantially wavelength to time mapping (ie, optical time stretching). In many embodiments of the invention, the overall spatial arrangement of the sub-beams is maintained after the time stretching operation, except that adjacent sub-beams can have differential delays relative to each other. Sub-beams can then be scanned across the sample being measured by appropriate relay optics. As far as the Type I spatial disperser is concerned, since it involves a spectral coding step, a wide frequency source is required.

A Type II spatial diffuser can also be considered to generate a sub-beam array. However, between sub-beams with different propagation angles, since the spatial dispersion for Type II is wavelength-independent, each sub-beam still maintains the same complete spectrum. The amount of delay for each sub-beam caused by the spatial cavity is completely dependent on the sub-beam propagation angle, regardless of the wavelength. Subsequently, the reflected sub-beams are successively separated in time; this is similar to the optical time stretching process except that the delay is not wavelength dependent, but angularly related. These reflected sub-beams can be used as scanning beams to scan across the sample being tested using relay optics behind the cavity. In the case of a Type II spatial disperser, the light source is not limited to a wide frequency, and the narrowband pulse source may also be a light source. This relaxes the stringent requirements for fragile and/or bulky ultra-short (wideband) laser sources and performs well even with low cost intensity modulated continuous wave (CW) laser sources with electronic optics components.

Figure 6 shows a schematic diagram of an apparatus according to an embodiment of the invention based on the type II spatial disperser used. Referring to Figure 6, similar to the arrangement shown in Figure 3, after reflection of the relay mirror 15, the collimating beam can be spatially dispersed using the cylindrical lens 14, while in other lateral dimensions, the beam can still be collimated. . A spatially diverging beam can be considered an array of sub-beams, each sub-beam propagating at a different angle. Similar to FIG. 3, the generated sub-beam array is optionally reshaped by a beamformer 3 (eg, a beam expander or compressor based on a compound lens system) before being coupled to the spatial cavity 4. The individual sub-beams of the sub-beam array can enter the spatial cavity at the fulcrum 7 at different angles of incidence. The delay mechanism can then be explained by Figure 2. After the double pass (enter and exit) of the cavity 4, the sub-beams with different angles of incidence can withstand different delays, as is the case with the Type I spatial diffuser shown in Figure 3.

In the case of a Type I spatial disperser, the angle of incidence of the sub-beams is spectrally encoded and the time delay between the sub-beams is substantially GDD. In contrast, with the Type II spatial disperser, the operation bypasses the spectral coding step. Thus, the amount of delay for each sub-beam caused by the spatial cavity can depend entirely on the sub-beam propagation angle (independent of wavelength) by the spatial diffuser configuration (eg, by using a simple lens to alter beam divergence). The Type I spatial disperser is capable of encoding the angle into separate spectral components, while the Type II spatial disperser is capable of directly defining the angle of the individual sub-beams, each sub-beam comprising the complete source spectrum. Each individual sub-beam maintains complete spectral content. Thus, the concept of using a Type II spatial disperser for time delay and thus beam scanning (described in more detail below) enables a higher frequency wide capacity of information encoding and allows for a wider range of operating wavelengths. Furthermore, since it does not require a spectral coding step, it is possible to produce a simplified passive beam scanning principle of operation, ie direct mapping delay to spatial scanning. This is different from the typical time stretching scheme that requires two steps of mapping (spectral coding and subsequent wavelength time mapping).

Although a cavity based on two-dimensional (2D) geometric optics has been described, embodiments of the invention are not limited thereto. Embodiments can be extended to a three-dimensional (3D) scheme to improve the compactness of the cavity. For example, a slow-converging cone-like cavity with a high reflectivity inner surface can be used. Figure 10 shows a schematic diagram of an embodiment of 2D limitation of N mirror spaces 啁啾 polygonal cavity. Figure 10A shows a top view of a square space cavity (N = 4) in which only one mirror (mirror 16) is angled. Thus, by way of example, when input light enters the mirror 17, light can travel down the cavity, in a helical helical trajectory 20, which is shown in Figure 10B, which is a side view of the display cavity. Upon normal incidence onto one of the mirrors (e.g., mirror 16), the light will travel along the cavity upward in a similar helix-like trajectory 21 and exit at mirror 19. Such a cavity is capable of effectively increasing the induced optical path. Figure 10C shows a top view of an octagonal cavity 22 (N=8) with a ray trace 22A. Furthermore, the geometry of the high reflector does not have to be the shape of a mirror. By careful engineering of the geometry of the surface, such as a snail-like cavity, non-linear (eg, quadratic) enthalpy in time can be achieved, resulting in greater freedom in designing pulse stretching/compression.

By mapping separate delay components to different spatial coordinates in the scan mode, the spatial cavity can be adapted for ultra-fast all-optical passive laser beam scanning along with the use of spatial beamformers. Referring to Figure 11, once the angular correlation delay is caused in the two-pass sub-beam from the cavity, the angularly swept sub-beam is transformed into a transverse scanning beam 24 by the relay optical system 23. Such a system can be configured in such a way that the fulcrum 7 of the cavity is on the Fourier plane of the final beam scanning plane (ie, the two planes should be in a spatial Fourier transformation relationship). In this case, the output sub-beam (ie, after the two-pass trajectory) can be extracted by an optical looper or optical splitter (both can be free-space or fiber-based components) and delivered to the sample under test . The mirror separation, the tilt of the mirror, and the angle of incidence of the sub-beams can all be dynamically tunable parameters. This creates the ability to actively manipulate the delay and thus the beam scan rate. Such active tunable delays caused by spatial chirps are also highly scalable.

Figure 12 shows a schematic diagram of an apparatus in accordance with an embodiment of the present invention in the context of laser beam scanning. Figure 12A shows an apparatus based on the type I spatial disperser 25 (e.g., diffraction grating) used, and Figure 12B shows an apparatus based on the type II spatial disperser 28 (e.g., lens) used. The dual pass sub-beam can be routed first by the beam splitter 26 and then by the telephoto lens system (e.g., in a 4-f configuration, as shown in Figure 12). This ensures that the final scan beam 24 is scanned across the sample laterally through the desired scan field of view, which can be controlled by the zoom-out of the telephoto system. In the imaging environment, as a general practice employed in imaging systems (Figs. 12A and 12B), the bright field/dark field information of the scanned points can be collected by photodetector 27.

Embodiments of the present invention are also compatible with fluorescence imaging, which has traditionally been inefficient in traditional time stretching or spectrally encoded imaging. This is because image signals collected in typical time stretch or spectrally encoded imaging follow the same spectrally encoded excitation path, making fluorescent detection inefficient. While additional frequency modulation and multi-channel detection schemes have been used for fluorescence spectrally encoded imaging, embodiments of the present invention are able to bypass the spectral encoding step (by using Type II spatial dispersers) and maintain ultra-fast speeds similar to temporal stretching. The advantage thus embodies a much more efficient solution for ultrafast fluorescent image detection. Referring to Figure 12C, for fluorescence imaging, an additional dichroic mirror 29 is required to separate the excitation wavelength from the fluorescence emission wavelength spectrum (Figure 12C shows an example of using a Type II spatial disperser).

The beam scanning provided by the spatial cavity can be in one dimension (1D), but depending on the application, the complete 2D imaging can be implemented by two different strategies: (i) 2D raster scanning scheme, where fast axis scanning Performing through the cavity, while slow axis (orthogonal axis) scanning is done by any type of high speed beam scanner, such as a resonant mirror (eg, approximately 10 kHz) or an acousto-optic deflector (AOD) (eg, approximately 100 kHz); A one-dimensional line scan for on-the-fly imaging in which high-speed one-way motion of a sample or source automatically provides one-dimensional image scanning. This is particularly relevant for applications such as imaging flow cytometry for high-throughput detection, ultra-large-scale integration (VLSI) semiconductor circuit wafer inspection and large-scale quality control and inspection in manufacturing for clinical diagnostics and basic life science research. Screening including fabric/paper is advantageous.

In an embodiment, an apparatus for stretching and/or compressing optical pulses can include: spatially dispersing a sub-beam array arranged to split a collimated optical pulse beam into sub-beams having equal (or approximately equal) spacing angles a beamformer configured to control the spread angle of the sub-beam array and a cavity that sequentially reflects individual sub-beams within the sub-beam array. The spatial disperser can for example be a spatial diffractive element.

The beamformer can include a 4F correlator, but embodiments are not limited thereto. Such 4F correlators can include two or more convex lenses with various focal lengths to control the individual angular separation between sub-beams within the sub-beam array.

The cavity can be a spatial cavity as described herein. The cavity can include two non-parallel inner surfaces (eg, a mirror). In a particular embodiment, the cavity can include only one inlet opening (eg, an entry point). The two inner surfaces of the cavity can each have a highly reflective coating. Depending on the optical path length difference/linearity of the time separation, the geometry of the two inner surfaces of the cavity can be flat or curved. The geometry of the two inner surfaces of the cavity can be three dimensional. The spacing between the two inner surfaces can be filled with air. The range of operation of the chamber and device can be any wavelength. The two inner surfaces can be arranged to have an inclination (A/m) that matches the angular spacing between the sub-beams of the sub-beam array. The convergence sub-beam array can enter the cavity through the entrance port. In some embodiments, individual sub-beams of the sub-beam array are capable of withstanding multiple reflections from the inner surface, and individual sub-beams of sub-beam arrays having integer multiples of inclination (A/m) N(ω) are capable of The inner surface reflects N(ω) times, wherein the angle of incidence of the individual sub-beams after each reflection can be reduced by A/m and eventually becomes perpendicular to the inner surface of the last reflection, wherein there are separate multiples of the dip The sub-beams are capable of withstanding different numbers of reflections, wherein individual sub-beams of different multiples of dip can be propagated with different optical path lengths, and wherein individual sub-beams with different multiples of dip can reverse the optical path and be spatially dispersed Re-merge.

Where the two inner surfaces of the cavity each have a highly reflective coating, the choice of highly reflective coating can be based on the center wavelength and bandwidth of the source.

The spatial disperser can be an optical diffraction grating, but the embodiment is not limited thereto. The spectral components of the optical pulse can be spatially extended to an approximately equally spaced angular sub-beam array.

The spectral components of the optical pulse can propagate in different optical path lengths induced by the cavity. The spectral components of the optical pulses can be spread over time due to different optical path lengths, equivalent to a certain amount of dispersion of the spectral components of the optical pulses.

The spatial disperser can be a cylindrical convex lens, but the embodiment is not limited thereto. In some embodiments, the spatial frequency component can be generated after the collimated pulse beam passes through the cylindrical convex lens, wherein the spatial frequency component initially converges before the focus of the cylindrical convex lens and is spread after the focus, and wherein the spatial frequency component Expanded into equally spaced angular beamlet arrays.

The spatial frequency components of the optical pulses are capable of propagating in different optical path lengths induced by the cavity. The spatial frequency components of the optical pulses can be expanded in time due to different optical path lengths, equivalent to dividing a single pulse into a matrix of sub-pulses.

In many embodiments, the methods of the present invention can include stretching and/or compressing one or more optical pulses over time using one or more devices described herein.

In many embodiments, the methods of the present invention can include the fabrication of one or more devices described herein using suitable materials.

The apparatus and method of the present invention can be used in a wide range of applications. They can be used not only for standard fiber optic telecommunications and for nonlinear optical imaging, but also for flexible dispersion compensation for visible light communication, an emerging field for indoor navigation and optical Wi-Fi. The related techniques include ineffective dispersion compensation techniques that can be employed in the visible spectrum. The present invention is particularly advantageous in view of the continuing need for increased data transfer rates. Additionally, embodiments of the present invention provide new paradigm shifts in allowing ultrafast spectroscopy and microscopy based on optical time stretching techniques ranging from, for example, ultraviolet to infrared wavelengths. Applications include, but are not limited to, high throughput cellular/tissue inspection, call analysis, toxic gas detection, and air pollution assessment through gas spectroscopy.

Embodiments of the present invention can benefit from bar code scanning, biomedical imaging, materials science research, laser beam processing and ablation, and automated surface inspection in manufacturing (including semiconductors in the VLSI industry) in the context of laser scanning applications. Integrated circuit (IC) wafer fabrication).

The apparatus and method of the present invention is capable of direct serial space time coding using the ordered delay characteristics of the spatial chirp. This feature enables high throughput and ultrafast optical imaging in any wavelength region that is not possible with fiber-based time stretching techniques. In addition, it allows for fluorescence time stretch imaging, and due to the lack of reliable time stretching techniques in the short wavelengths (ie, ultraviolet (UV) to visible and near infrared) where many established fluorescent bioimaging techniques operate, This has been impossible with any relevant technical time stretching imaging modalities. Furthermore, spectral coding is generally inefficient for fluorescent detection (de-scanning and therefore generally prohibits standard confocal detection). Embodiments of the present invention allow for ultra-fast fluorescence imaging along with its large stretching time and low loss operation.

Moreover, if a Type II spatial diffuser is used, embodiments can simplify time stretch imaging (i.e., can bypass spectral coding) by relaxing the requirements for broadband pulse sources. This results in a more efficient bandwidth coding, and thus allows color imaging (eg, wavelengths in the UV, visible, and near-out-of-work) to be performed simultaneously using multiple wavelength region pulse sources. Embodiments also allow for mid-infrared (intermediate IR) applications, in particular, because no high-speed image arrays are available in the medium IR, speeding up imaging and spectroscopy (eg, for far-end sensing) is accelerated.

Techniques have been developed to achieve group delay dispersion (GDD) using optical diffraction elements (e.g., diffraction grating pairs) or spatially dispersed elements (e.g., prism pairs) to bypass the use of optical fibers to perform time pulse stretching and compression. Such techniques suffer from large insertion loss, limited amount of dispersion, or both, which explains why they are only used for applications requiring fine GDD adjustment in a narrow range (between femtoseconds and picoseconds only). Examples of such techniques include pulse shaping for nonlinear optical microscopy for bioimaging applications and pulse "pre-twist" prior to fiber delivery to prevent unwanted non-influence of signal fidelity in fiber optic communication. Linear effect. Embodiments of the present invention overcome these challenges by providing a novel concept for achieving highly scalable and flexible tuning (or GDD) of dispersion that can operate in an unprecedented wide wavelength spectrum (e.g., from ultraviolet to infrared) . The dispersion that the present invention can provide can be superior to the current technology.

Techniques for performing high-speed passive beam scanning based on a two-step scheme have been developed: (1) pulse stretching (dispersion Fourier transform or simply optical time stretching), ie, based on dispersion - due to the difference in refractive index of the medium, broadband The phenomenon that different wavelength (frequency) components of light propagate at different speeds, stretching the spectral information over time into the serial time signal; and (2) spectral coding, ie by using a one- or two-dimensional spatial diffuser, The different wavelengths (frequencies) of the spectrum of the broadband source are scattered spatially in different spatial coordinates. Passive beam scanning using this technique is much faster than spectrally coded beam scanning as discussed in the background section above, since it is entirely controlled by the repetition rate of a pulsed laser typically at about MHz or even GHz.

Embodiments of the present invention provide high speed laser beam scanning with a scan rate of up to MHz or even GHz controlled only by the repetition rate of the laser source. This is orders of magnitude faster than any related active or passive beam scanning technology. The beam scanning performance of the present invention is not affected by mechanical instability and fatigue, allowing for long-term stable operation.

In many embodiments of the invention, the range of beam deflection angles is determined only by the relay optics, rather than by the cavity itself. Thus, it is capable of flexible tuning and achieves a wide deflection angle that overcomes the trade-off between scan rate and deflection angle in related art scanning techniques (eg, galvanometer mirrors, AOD and EOD). In addition, the resolvable scan points can be adjusted over a wide range from 10 to 100 by engineering the geometry of the cavity. This is independent of the scan rate (which can be controlled by the repetition rate of the laser source), thereby overcoming the trade-off between scan rate and resolvable scan points in related art scanning techniques (eg, AOD and EOD).

Embodiments of the present invention address several of the problems exhibited by the related art passive scanning techniques (e.g., time stretch imaging modalities based on Decentralized Fourier Transform). The invention can be used not only for a broadband ultrashort pulse laser source (generally vulnerable, bulky and costly), but also compatible with an intensity modulated CW laser source (in the case of a Type II space disperser), thereby making it ultrafast Beam scanning technology has greatly expanded the choice of light source. This in turn suggests that multiple light sources can be wavelength multiplexed to perform color imaging, which is not present in technical time stretch or spectrally encoded imaging modalities. Furthermore, the present invention is capable of producing extremely large GDDs compared to large GDD operations in optical time stretching by optical fibers, and since the operation can be performed entirely in free space, it does not suffer from optical loss due to material scattering and absorption. . Therefore, it is not limited to any particular operating wavelength window typically present in the fiber, allowing for all optical passive beam scanning from the UV to the IR range. Therefore, it is a versatile technology that can be applied to optical bioimaging, bar code scanning, remote sensing, biomedical imaging, materials science, laser beam processing and ablation, and automated surface inspection in manufacturing (including in the VLSI industry). Manufacturing of semiconductor IC chips). Additionally, the present invention allows for dynamic tuning of delay separation between individual sub-beams, at least in part due to the free space design of the cavity. The time delay separation can be made large enough to resemble or be longer than the fluorescent lifetime of a typical fluorescent molecule/probe widely used in biological and biochemical research, thereby enabling the device to be configured to perform laser scanning at an unprecedented imaging rate. Fluorescence imaging. Since time stretch imaging has long been considered incompatible with fluorescence imaging, this is an important feature.

All patents, patent applications, provisional patents, and publications (including those in the "References" section) cited or recited herein are hereby incorporated by reference in its entirety as if The figures and tables are so limited that they do not contradict the explicit teachings of this specification.

 Exemplary embodiment  

The invention includes, but is not limited to, the following examples.

Embodiment 1. An apparatus for stretching/compressing optical pulses, comprising: a spatial disperser arranged to split a collimated optical pulse beam into sub-beam arrays of sub-beams having equal spacing angles; a beamformer configured to Controlling an extended angle of the sub-beam array; and a cavity configured to sequentially reflect individual sub-beams within the sub-beam array.

Embodiment 2. The apparatus of embodiment 1, wherein the spatial disperser is a spatial diffractive element.

The apparatus of any of embodiments 1-2, wherein the beamformer comprises a 4F correlator.

Embodiment 4. The apparatus of embodiment 3, wherein the 4F correlator comprises two or more convex lenses having various focal lengths to control a separate angular separation between the sub-beams within the sub-beam array.

The device of any of embodiments 1-4, wherein the cavity is a spatial cavity.

The device of any of embodiments 1-5, wherein the cavity comprises two non-parallel inner surfaces.

The device of any of embodiments 1-6, wherein the chamber comprises only one inlet port.

The device of any of embodiments 6-7, wherein the two inner surfaces of the cavity each have a highly reflective coating.

Embodiment 9. The apparatus of any of embodiments 6-8, wherein the geometry of the two inner surfaces of the cavity is dependent on linearity of optical path length/time separation.

Embodiment 10. The apparatus of any of embodiments 6-9, wherein the geometry of the two inner surfaces of the cavity is flat.

Embodiment 11. The apparatus of any of embodiments 6-9, wherein the geometry of the two inner surfaces of the cavity is curved.

Embodiment 12. The apparatus of any of embodiments 6-11, wherein the geometry of the two inner surfaces of the cavity is three-dimensional.

Embodiment 13. The apparatus of any of embodiments 6-12, wherein the spacing between the two inner surfaces is filled with air.

Embodiment 14. The device of any of embodiments 1-13, wherein the operating range of the device is any wavelength.

Embodiment 15. The device of any of embodiments 1-13, wherein the device operates from ultraviolet to infrared wavelengths.

Embodiment 16. The apparatus of any of embodiments 6-15, wherein the two inner surfaces are arranged to have an inclination (A/m) that matches an angular separation between sub-beams of the sub-beam array.

The device of any of embodiments 1-16, wherein the converging sub-beam array enters the cavity through the entrance of the cavity.

Embodiment 18. The apparatus of any of embodiments 6-17, wherein the individual sub-beams of the sub-beam array are subjected to a plurality of reflections from the inner surface with an integer multiple of the tilt angle (A/m) N(ω The individual sub-beams of the sub-beam array are reflected N(ω) times from the inner surface of the cavity, wherein the angle of incidence of the individual sub-beams can be reduced by A/m after each reflection, and eventually becomes perpendicular to the inner surface of the last reflection , in which individual sub-beams with different multiples of inclination are subjected to different numbers of reflections, wherein individual sub-beams with different multiples of inclination can propagate through different optical path lengths, and individual sub-beams with different multiples of inclination can Reverse the optical path and recombine in the spatial diffuser.

Embodiment 19. The apparatus of any of embodiments 8-18, wherein the highly reflective coating is selected based on a center wavelength and a bandwidth of the light source.

The apparatus of any of embodiments 1-19, wherein the spatial diffuser is a spatial diffraction grating.

Embodiment 21. The apparatus of embodiment 20 wherein the spectral components of the optical pulses spatially extend to an approximately equally spaced angular sub-beam array.

Embodiment 22. The apparatus of any of embodiments 18-21, wherein the spectral components of the optical pulses propagate in different optical path lengths induced by the cavity.

Embodiment 23. The apparatus of Embodiments 18-21 wherein the spectral components of the optical pulses are time-expanded due to different optical path lengths, and the spectral components equivalent to the optical pulses are subject to a certain amount of dispersion.

The apparatus of any of embodiments 1-23, wherein the spatial disperser is a cylindrical convex lens.

Embodiment 25. The apparatus of embodiment 24, wherein the spatial frequency component is generated after the collimated pulse beam passes through the cylindrical convex lens, wherein the spatial frequency component initially converges before the focus of the cylindrical convex lens and is dispersed after the focus, and The spatial frequency component is extended to an equally spaced angular sub-beam array.

Embodiment 26. The apparatus of any of embodiments 18-25, wherein the spatial frequency component of the optical pulse propagates in a different optical path length induced by the cavity.

Embodiment 27. The apparatus of any of embodiments 18-25, wherein the spatial frequency component of the optical pulse expands in time due to different optical path lengths, equivalent to dividing a single pulse into a matrix of sub-pulses.

Embodiment 28. The apparatus of any of embodiments 1-27, capable of high speed laser beam scanning at a scan rate of about MHz, wherein the scan rate is controlled only by the repetition rate of the laser source.

Embodiment 29. The apparatus of any of embodiments 1-27, capable of high speed laser beam scanning at a scan rate of about GHz, wherein the scan rate is controlled only by the repetition rate of the laser source.

The device of any of embodiments 1-29, wherein the device is configured to allow for dynamic tuning of delay separation between individual sub-beams.

Embodiment 31. The apparatus of embodiment 30, wherein the time delay separation between the individual sub-beams is sufficiently large such that the apparatus is configured to perform laser-scanning fluorescence imaging.

Embodiment 32. The apparatus of any of embodiments 1-27 and 30-31, further comprising a laser source for laser beam scanning, wherein the device is configured to be in the order of megahertz (MHz) or gigahertz (GHz) The scan rate performs high speed laser beam scanning, and wherein the scan rate is only controlled by the repetition rate of the laser source.

Embodiment 33. The apparatus of any of embodiments 1-32, wherein the range of beam deflection angles of the apparatus does not affect the cavity such that the range of beam deflection angles is flexibly tunable.

The device of any of embodiments 1-33, wherein the amount of resolvable scanning points of the cavity is determined by the geometry of the cavity.

Embodiment 35. The apparatus of any of embodiments 28, 29, and 32, wherein the laser source is a broadband ultrashort pulse laser source or an intensity modulated CW laser source.

Embodiment 36. The apparatus of any of embodiments 1-35, comprising a plurality of laser sources that provide optical pulses, wherein the apparatus is configured to wavelength multiplex a plurality of light sources to perform color imaging.

The device of any of embodiments 1-36, wherein the device is configured to perform an optical passive beam scan from an ultraviolet wavelength to an infrared wavelength.

The following is an example showing a process for practicing the present invention. These examples should not be considered limiting.

 Example 1  

Optical stretching of a commercial mode locking laser from a 20 MHz repetition rate is time stretched using two schemes: (1) using a long common dispersion fiber (5 kilometers), and (2) using an implementation in accordance with the present invention For example, a cavity with a size of 4 cm x 7 cm (mirror separation x mirror length) (based on a Type I space diffuser). The optical pulse from the laser is initially spectrally broadened into a transform-limited optical pulse by a nonlinear effect called self-phase element modulation, as shown by the curved dashed line in FIG. By using the apparatus of the present invention, the output spectrum captured by a conventional spectrometer (solid line) shows that almost the entire input spectrum can be maintained while spectral distortion is minimized.

To further examine the total GDD induced by the device of the present invention, the output signal is captured by an 80 Gb/s instant oscilloscope to observe the time spread of the optical pulses. Figure 5A shows a graph of a time stretched optical signal stretched by a dispersed fiber, and Figure 5B shows a graph of a time stretched optical signal stretched by the device of the present invention. Referring to Fig. 5A, a 5 km long ordinary dispersion fiber can achieve a total group velocity dispersion of 0.15 ns/nm, causing the spectrum of the pulse to be mapped into time by pulse stretching. Pulse stretching is the result of (material) dispersion of the glass fibers. In contrast, the device of the present invention does not rely on dispersion to achieve pulse stretching. In fact, the free-space optical path difference controlled by the geometric design of the cavity is mapped to the time domain. Referring to Figure 5B, the apparatus of the present invention has a total group velocity dispersion of up to 0.5 ns/nm and a total loss of 18 dB, which is mainly due to the limitation of the mirror length.

 Example 2  

The arrangement shown in Figure 6 is also based on the use of a Type II space diffuser. Figure 8A shows a single input pulse initiated to setup, which stretches it into a long envelope of pulse trains. Figure 8B shows the pulse train. Referring to Figures 8A and 8B, a single pulse is spread into an envelope of a pulse train of width 2.5 ns, and the number of valid primitives exceeds 60. Assuming that there are enough primitives that can be used to encode spatial information into the pulse train, this pulse train can also be used to perform another mode of time stretch imaging (in bright field imaging mode), which is no longer dependent Spectral coding, and therefore does not rely on dispersion.

 Example 3  

The setup shown in Figure 12B is based on a laser scanning setup of a spatial cavity and a Type II spatial diffuser for capturing bright field images. Fig. 13 shows a representative bright field image thus captured (Fig. 13A: resolution target; Fig. 13B: lung tissue section). The center wavelength of the illumination is approximately 710 nm. Press the send repetition rate (ie scan-scan) to 80MHz. The cavity provides a one-dimensional scan of the fast axis, while the slow axis scan is accomplished by converting the resolution target along the orthogonal axis. Ultrafast scans are done by direct spatiotemporal mapping, unlike the two-step mapping employed in the technical time stretch imaging modality.

It should be understood that the examples and embodiments described herein are for illustration only, and that various modifications and changes can be made by those skilled in the art, and such modifications and changes are intended to be included within the spirit and scope of the present application. Within the scope of the claims. In addition, any element or limitation of any invention disclosed herein or any embodiment thereof can be combined with any other element or limitation of the invention disclosed herein or any other element or combination thereof (alone or in any combination), and all such Combinations are considered in accordance with the scope of the invention and are not intended to be limiting.

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Claims (15)

 An apparatus for stretching/compressing optical pulses, comprising: a spatial disperser arranged to split a collimated optical pulse beam into sub-beam arrays of sub-beams having equal spacing angles; a beamformer configured to control the sub-beams An extended angle of the beam array; and a cavity configured to reflect the individual sub-beams within the sub-beam array in sequence and spatially, and to provide a space-time mapping of the pulse to a spatial domain directed to a physical object component.    The device of claim 1, wherein the cavity is a spatial cavity, wherein the two inner surfaces that are non-parallel and reflective form a 2D cavity or a 3D cavity.    The apparatus of claim 2, wherein the spacing between the two inner surfaces is filled with air, thereby allowing for dynamic tuning of the delay separation between the individual sub-beams.    The apparatus of claim 1, wherein the operation of the apparatus ranges from an ultraviolet wavelength to an infrared wavelength.    The apparatus of claim 2, wherein the two inner surfaces are arranged to have an inclination (A/m) that matches the equally spaced angles between the sub-beams of the sub-beam array.    The device of claim 5, wherein the individual sub-beams of the sub-beam array are subjected to a plurality of reflections from the inner surface with an integer multiple of the tilt angle (A/m). The individual sub-beams of the sub-beam array are reflected N times from the inner surface of the cavity, wherein the angle of incidence of the individual sub-beams after each reflection can be reduced by A/m and eventually become vertical The inner surface of the last reflection, wherein the individual sub-beams with different multiples of the tilt angle are subjected to different numbers of reflections, wherein the individual sub-beams with different multiples of the tilt angle can propagate through different optical path lengths, and The individual sub-beams with different multiples of the tilt angle are capable of reversing the optical path and recombining at the spatial diffuser.    The apparatus of claim 1, wherein the spatial disperser is a spectrally encoded free space disperser such as, but not limited to, a cylindrical convex lens, wherein the collimated pulse beam is generated after passing through the cylindrical convex lens a spatial frequency component, wherein the spatial frequency component initially converges before a focus of the cylindrical convex lens and is dispersed after the focus, and wherein the spatial frequency component extends into the sub-beam array, or a spectral coding space A diffuser, such as but not limited to a diffraction grating, wherein a spectrally encoded spatial frequency component is generated after the collimated pulse beam passes the diffraction, and wherein the spectrally encoded spatial frequency component is expanded into the sub-beam array.    The apparatus of claim 6 or 7, wherein the spatial frequency component of the optical pulse propagates in different optical path lengths induced by the cavity.    The apparatus of claim 6 or 7, wherein the spectrally encoded spatial frequency component of the optical pulse is temporally expanded due to the different optical path length, and the spatial frequency component equivalent to the optical pulse is subjected to A certain amount of dispersion.    The apparatus of claim 6 wherein the spatial frequency component of the optical pulse propagates in different optical path lengths induced by the cavity.    The apparatus of claim 6, wherein the spatial frequency component of the optical pulse is time-expanded due to the different optical path lengths, equivalent to dividing a single pulse into a matrix of sub-pulses.    The apparatus of any one of claims 1 to 11, wherein the apparatus is configured to perform an all-optical beam scan of the pulse in a spatial domain by introducing a delay between the individual sub-beams , perform a space time mapping.    The device of claim 12, further comprising a relay optical element that projects the scan beam onto the imaging sample.    The device of claim 12, further comprising a single or multiple light sources to provide optical pulses, wherein the device is configured with monochromatic or multi-color laser scanning fluorescence imaging and color imaging.    The apparatus of any one of claims 1 to 14, wherein the optical pulses are generated from a plurality of broadband ultrashort pulse laser sources or a single source of intensity modulated continuous wave laser sources.