Passive on-chip optical long-pass filter

Abstract

A passive on-chip optical long-pass filter is used for removing short-wavelength residual pump photons after photons are non-linearly generated. Depositing a thin layer (lt; the invention relates to non-crystalline silicon or polycrystalline silicon (e.g., 100 nm) to absorb light having a wavelength of about 1.1 [mu] m shorter than the silicon band gap wavelength, while the absorption loss of non-linearly generated light having a wavelength longer than the silicon band gap wavelength during propagation in the waveguide can be negligible. The filter is suitable for non-linear and quantum photon chips so as to achieve the on-chip optical pump light suppression ratio exceeding 120 dB. The filter is simple in design in concept, can be manufactured through a CMOS (Complementary Metal Oxide Semiconductor) process, and has potential high wafer level expandability and low-cost manufacturability. The filter can be realized in various integrated photon platforms, including silicon carbide, silicon nitride, lithium niobate and aluminum nitride.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 513,349, filed on July 12, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0003] Abbreviations

[0004] 3C-SiC Cubic Silicon Carbide

[0005] 3C-SiCoI 3C-SiC on Insulator

[0006] α-Si Amorphous Silicon

[0007] ALD Atomic Layer Deposition

[0008] AlN Aluminum Nitride

[0009] AlNoI AlN on Insulator

[0010] Al2O3 Alumina

[0011] c-Si Crystalline Silicon

[0012] CMOS Complementary Metal Oxide Semiconductor

[0013] CVD Chemical Vapor Deposition

[0014] DRIE Deep Reactive Ion Etching

[0015] EME Eigenmode Expansion

[0016] ER Extinction Ratio

[0017] IL Insertion Loss

[0018] LN Lithium Niobate

[0019] LNoI LN on Insulator

[0020] LPF Long Pass Filter

[0021] NIR Near Infrared

[0022] OSA Optical Spectrum Analyzer

[0023] poly-Si

[0024] SEM Scanning Electron Microscope

[0025] SiC Silicon Carbide

[0026] SiCoI SiC on Insulator

[0027] SPD Single Photon Detector

[0028] SPDC Spontaneous Parametric Down Conversion

[0029] TE Transverse Radio Wave

[0030] TM Transverse Magnetic Wave

[0031] UMZI Unbalanced Mach-Zehnder Interferometer Technical Field

[0032] The present application relates to an optical filter for long-pass filtering an incident light beam, a light conversion device for generating an output light beam from an input laser beam using the optical filter, and an optical system that can be implemented on an integrated photonic platform and uses the light conversion device. Background Art

[0033] Monolithic nonlinear and quantum photonic chips are expected to enable technological applications in a compact footprint without losing photons due to inter-chip coupling losses. Nonlinear chips may enable on-chip wavelength conversion, while quantum chips enable quantum state preparation and manipulation functions, including quantum metrology, quantum communication, and quantum computing.

[0034] On-chip nonlinear and quantum light sources have been demonstrated as key integrated components on various material platforms and through different photon generation processes. Single photon emission from color centers has been demonstrated in integrated SiCoI platforms (the SiC used in the platform is 4H-SiC [1], [2]) and suspended 3C-SiC resonators [3], [4]. These color centers apply shorter wavelength pump lasers and emit photons at NIR wavelengths. Nonlinear and photon pair sources based on second-order optical nonlinearity have been demonstrated on integrated 3C-SiCoI platforms [5], [6], integrated AlNoI platforms [7] and LNoI platforms [8]. Photon pair sources down-convert pump light at a wavelength of 780 nm into photon pairs at a wavelength of 1550 nm through SPDC. SPDs operating at low temperatures using niobate nitride nanowires have been demonstrated on various heterogeneous integrated material platforms [9],

[10] .

[0035] In addition to on-chip nonlinear and quantum light sources and SPDs, on-chip pump suppression filters are also essential building blocks for integrated quantum photonic circuits, but they are relatively less studied in the field. Excess on-chip pump photons must be removed before interacting with downstream components and photon detection. For example, a reasonable photon count rate of 1 MHz is generated, which is about 120 dB weaker than the on-chip pump power of 1 mW. By cascading multiple stages of optical microring filters

[10] or Mach-Zehnder interferometers

[11] , tens of dB of wavelength selective isolation can be achieved. However, these wavelength-flexible cascaded filters restrict single photon and photon pair sources to narrow spectral bands. These filters further impose careful active wavelength alignment between all individual filter stages. Using active thermal and electrical control to align the filter wavelength consumes additional energy and computational resources. Long gratings

[12] , directional coupler-based filters with integrated gratings

[14] , and tapered waveguides

[15] can achieve reasonable ER and relatively wide bandwidth. However, these designs still require cascading carefully designed filter stages, which often increases IL and requires precision manufacturing processes.

[0036] There is a need in the art for an improved design that does not require precision manufacturing processes while achieving higher ER values. Summary of the invention

[0037] The first aspect of the present disclosure is to provide an optical LPF, which is used to perform long-pass filtering on an incident light beam to produce a filtered light beam. The incident light beam includes a desired light component and an undesired light component. The desired light component has one or more first component wavelengths. The undesired light component has one or more second component wavelengths. Each wavelength of the one or more first component wavelengths is longer than each wavelength of the one or more second component wavelengths.

[0038] The filter includes a waveguide core and a selective absorption layer. The waveguide core is used to receive an incident light beam, propagate a desired light component and an undesired light component inside the waveguide core, and output a filtered light beam. The selective absorption layer is deposited on the waveguide core. The selective absorption layer is composed of an indirect bandgap semiconductor material, which is selected to have a bandgap energy greater than the maximum photon energy associated with one or more first component wavelengths and less than the minimum photon energy associated with one or more second component wavelengths, so that when the desired light component and the undesired light component interact with the selective absorption layer during propagation inside the waveguide core, the undesired light component is attenuated while the optical power of the desired light component is retained.

[0039] Note that the filter is formed by a simple process of depositing a selective absorption layer on the waveguide core. This simple filter manufacturing process alleviates the need for precision processes in the filter manufacturing process. In addition, the use of indirect bandgap semiconductor materials to absorb undesirable light components while retaining the desired light components can achieve high ER values.

[0040] In some embodiments, the indirect bandgap semiconductor material is selected to be α-Si or poly-Si. The thickness of the selective absorption layer may be less than or equal to 100 nm.

[0041] In certain embodiments, the waveguide core is implemented in the form of a strip waveguide.

[0042] In certain embodiments, the waveguide core is realized in the form of a rib waveguide.

[0043] In certain embodiments, the waveguide core is composed of 3C-SiC.

[0044] In certain embodiments, the waveguide core is composed of a material selected from the group consisting of SiC, LN, and AlN.

[0045] In some embodiments, the filter further comprises an optical insulator layer, the waveguide core is located on the optical insulator layer, and the optical insulator layer provides a first reflection interface between the waveguide core and the optical insulator layer to reflect the desired light component during propagation of the desired light component inside the waveguide core.

[0046] In certain embodiments, the optical insulator layer is composed of SiO2.

[0047] In certain embodiments, the respective materials forming the optical insulator layer and the waveguide core are selected to allow total internal reflection of the desired light component at the first reflective interface.

[0048] In some embodiments, the filter further comprises a cladding layer, which is deposited on a combination of at least the selective absorption layer and the waveguide core. In particular, the cladding layer is an optical insulator cladding layer that provides a second reflection interface between the waveguide core and the optical insulator cladding layer to reflect the desired light component during propagation of the desired light component inside the waveguide core.

[0049] In certain embodiments, the cladding is comprised of SiO2.

[0050] In certain embodiments, the waveguide core is shaped to be straight.

[0051] In certain embodiments, the waveguide core is shaped to be curved.

[0052] In certain embodiments, the selective absorption layer is shaped so that a non-filtering section of the waveguide core abruptly transitions to a filtering section thereof, wherein the filtering section is a first longitudinal section of the waveguide core, the first longitudinal section being completely covered by the selective absorption layer, and the non-filtering section is a second longitudinal section of the waveguide core, the second longitudinal section being completely not covered by any selective absorption layer.

[0053] In some embodiments, the longitudinal end of the selective absorption layer has an inclined profile that covers a transition region between a non-filtering section and a filtering section of the waveguide core, so that the non-filtering section gradually transitions to the filtering section.

[0054] In some embodiments, the longitudinal end of the selective absorption layer has a primary tapered profile, which covers the transition region so that the non-filtering section gradually transitions to the filtering section.

[0055] In some embodiments, the longitudinal end of the selective absorption layer has a two-stage tapered profile overlying the transition region so that the non-filtering section gradually transitions to the filtering section.

[0056] A second aspect of the present disclosure is to provide a light conversion device for generating an output light beam from an input laser beam.

[0057] The optical conversion device includes one or more nonlinear quantum light sources, which are collectively configured to perform SPDC on an input laser beam to nonlinearly generate a first light beam, so that the first light beam includes a desired light component and an undesired light component. The desired light component has one or more first component wavelengths. The undesired light component has one or more second component wavelengths. Each wavelength of the one or more first component wavelengths is longer than each wavelength of the one or more second component wavelengths. The optical conversion device also includes any embodiment of the optical long-pass filter disclosed above, which is used to perform long-pass filtering on the first light beam to produce an output light beam. The first light beam is regarded as an incident light beam, and the filtered light beam is regarded as an output light beam.

[0058] A third aspect of the present disclosure is to provide an optical system.

[0059] The optical system comprises any one of the embodiments of the light conversion device disclosed above. In addition, the optical system further comprises one or more photonic circuits for processing the output light beam.

[0060] In certain embodiments, the optical system is implemented as an integrated photonic chip.

[0061] Other aspects of the present disclosure are disclosed as shown in the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1A prototype LPF is depicted, which is implemented as an α-(poly-)Si based on-chip LPF for an integrated SiCoI quantum photonic platform.

[0063] Figure 2 A top view and a cross-sectional view of a prototype LPF used in a proof-of-concept experiment are schematically depicted, showing the structure of the prototype LPF.

[0064] Figure 3 The IL results of the prototype LPF for simulated transmission of TE and TM polarization modes at wavelengths of 1550nm and 780nm are plotted at a filter length of 1mm.

[0065] Figure 4 The simulated mode field amplitude distributions of the TE and TM polarization modes of the 780nm and 1550nm beams transmitted within the first 10μm of the waveguide in the internal propagation direction of the prototype filter are plotted for different silicon layer thickness values.

[0066] Figure 5 The fabrication process flow for making the prototype LPF sample is depicted.

[0067] Figure 6 Two images of the fabricated prototype LPF are shown, where Figure 6 Sub-figure (a) is an image of fabricated filters with different filter lengths, and sub-figure (b) thereof shows a SEM image of the transition region from waveguide to filter.

[0068] Figure 7 The lens-to-lens normalized transmission spectra for TE and TM polarizations at different filter lengths used in the prototype LPF are shown, where: sub-figures (a) and (b) show the corresponding spectra obtained for TE polarization and TM polarization, respectively; sub-figures (c) and (d) show the corresponding spectra for TE polarization and TM polarization at 780nm wavelength (765nm to 795nm), respectively; sub-figures (e) and (f) are near-field images of the output butt coupler obtained from the reference waveguide (with 0μm length filter) and the waveguide with 100μm length filter; sub-figure (g) shows the wavelength-averaged transmission gain in three wavelength windows (1550 / 1310 / 780nm) for TE and TM polarizations at different filter lengths.

[0069] Figure 8 The output spectra captured by the OSA with and without 780nm pump light coupled into the prototype LPF with a length of 100μm are plotted, showing that no re-emission exceeding the -90dB level occurs under 1mW on-chip pump power conditions.

[0070] Fig. 9Depicted are a top view, a longitudinal cross-sectional view, and a side cross-sectional view of an optical LPF according to an exemplary embodiment of the present disclosure.

[0071] Figures 10A to 10D Some embodiments of the disclosed optical LPF are depicted in side cross-sectional view, wherein:

[0072] Fig. 10A As a reference, the Fig. 9 A first LPF of an exemplary embodiment of an optical LPF disclosed in , wherein an air cladding is used in the first LPF, and a waveguide core of the first LPF is a strip waveguide;

[0073] Fig. 10B depicts a second LPF obtained from the first LPF by using a rib waveguide instead of a strip waveguide as a waveguide core;

[0074] Fig. 10C depicts a third LPF obtained from the first LPF by further including a cladding layer deposited on the selective absorption layer and the waveguide core; and

[0075] Fig. 10D Depicted is a fourth LPF formed from the first LPF by using a rib waveguide instead of a strip waveguide as a waveguide core and by including a cladding.

[0076] Fig.11A and 11B Two further embodiments of the disclosed optical LPF are depicted, wherein:

[0077] Fig.11A depicts a fifth LPF having a straight waveguide core; and

[0078] Fig. 11B Depicted is the sixth LPF with a bent waveguide core.

[0079] Figures 12A to 12D Some waveguide-to-filter transition designs for the disclosed optical LPF are depicted, where:

[0080] Fig. 12A An abrupt transition is shown;

[0081] Fig. 12B The tilt transition is shown;

[0082] Fig. 12C A primary tapered transition is shown; and

[0083] Fig.12D A two-stage tapered transition is shown.

[0084] Fig.13A schematic diagram of an exemplary embodiment of a disclosed optical system is depicted, wherein the optical system includes a light conversion device including the disclosed optical LPF.

[0085] Those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. DETAILED DESCRIPTION

[0086] The present disclosure will be described more fully below with reference to the accompanying drawings. However, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0087] The present disclosure relates to an optical LPF for long-pass filtering an incident light beam, a light conversion device for generating an output light beam from an input laser beam using the optical LPF, and an optical system that can be implemented on an integrated photonic platform and employs the light conversion device.

[0088] The inventors developed the disclosed optical LPF through the following observations. Indirect bandgap semiconductor materials are natural LPFs or absorbers for short wavelengths because they provide reasonable absorption of photons with energies exceeding their bandgap without efficient radiative recombination. For centimeter-scale photonic chips, the intrinsic material absorption of light within the transparent window of these indirect bandgap semiconductor materials is negligible. Among the readily available conventional semiconductor materials, α-Si and poly-Si are promising candidates because both materials have a bandgap of about 1.14 eV and absorb visible / NIR pump light with wavelengths shorter than 1.1 μm, while both materials are largely transparent to light in the telecom O, C, and L bands. α-(poly-)Si materials can be easily deposited on substrates using CVD furnaces in CMOS factories. Compared with c-Si, α-(poly-)Si materials have higher structural disorder and thus provide a larger state density than c-Si

[16] . In the visible spectrum, the absorption coefficient of α-Si is about an order of magnitude larger than that of c-Si

[17] . It is known that deposition temperatures above 680°C will cause α-Si to partially crystallize into poly-Si, thereby weakening its absorption capacity

[17] . Since α-Si has better light absorption than poly-Si and its deposition process on wafers is simple and low-cost, α-Si has been widely used in solar cells

[18] . α-Si materials are also deposited on silicon nitride photonic platforms and used as on-chip microheaters because the absorbed light can be converted into heat

[19] .

[0089] The inventors have also observed that the disclosed optical LPF can be manufactured by a simple process of depositing thin films of α-(poly-)Si layers. Advantageously, no precision processes are required to manufacture the disclosed optical filter.

[0090] In this disclosure, a prototype LPF is first provided as a representative case to illustrate the claimed invention. The prototype LPF is a passive on-chip pump suppression LPF designed to filter out the 780nm pump light component in a polychromatic beam with 780nm and 1550nm light components, and is integrated on an integrated photonic platform. Then, the details of the prototype LPF will be summarized to develop the claimed invention.

[0091] A. Prototype LPF

[0092] The prototype LPF utilizes a thin film α-(poly-)Si layer (less than 100 nm thick) deposited on the top surface and sidewalls of an integrated waveguide to block pump light in the visible / NIR wavelengths shorter than 1.1 μm by intrinsic material absorption along the waveguide propagation direction, while nonlinearly generated, longer NIR wavelength (signal and idler) light in the transparent window of the film still propagates without significant absorption or mode perturbation. Such a waveguide structure with a properly designed absorption film thickness provides a pump suppression ratio of more than 120 dB within a compact filter length of 1 mm. The prototype LPF is suitable for the purpose of efficient on-chip pump suppression on integrated quantum photonic chips.

[0093] Figure 1 A schematic diagram of a prototype LPF (labeled 100) is depicted, implemented as an α-(poly-)Si-based on-chip LPF for an integrated SiCoI quantum photonic platform. The prototype LPF 100 is formed by an integrated waveguide structure 110 for guiding and propagating an incident light beam 181. The incident light beam 181 consists of a signal light, an idler light, and a pump light. The signal light and the idler light are light components with wavelengths longer than 1100nm, while the pump light is another light component with a wavelength shorter than 1100nm. A thin layer 120 of α-(poly-)Si is deposited on a section of the integrated waveguide structure 110 to gradually absorb the pump light without attenuating the signal light and the idler light, or only attenuating the signal light and the idler light negligible. Therefore, the waveguide structure 110 outputs a filtered light beam 182 having only the signal light and the idler light. The waveguide structure 110 can be fabricated on a variety of material platforms, including SiC, LN, and AlN. The optical insulator layer 130, which has a lower refractive index than the waveguide material, is used to confine the signal light and the idler light by total internal reflection, and can be made of various materials. Light beams of different wavelengths propagate in different light modes in the waveguide structure 110, with different spatial distributions. Light beams with wavelengths shorter than about 1.1 μm that overlap with the absorption region of the α-(poly-)Si layer are strongly attenuated.

[0094] Note that if the waveguide structure 110 is appropriately designed to have a curved shape, the footprint of the prototype LPF 100 can be made compact. Figure 1 In the example shown in FIG. 1 , the waveguide structure 110 has a meandering shape to save space. Note that other shapes may also be used to form the waveguide structure 110. A straight waveguide may also be used.

[0095] A proof-of-concept experiment was performed to validate the prototype LPF 100 on the 3C-SiCoI platform.

[0096] A.1.LPF Design

[0097] Figure 2 A top view and a cross-sectional view of the prototype LPF 100 are schematically depicted to illustrate its structure. During the design process, a 3C-SiC waveguide with a width, SiC film thickness, and plate thickness of 850nm, 460nm, and 100nm, respectively, was used to implement the waveguide structure 110. Based on the device manufacturing results, a waveguide sidewall slope of about 80° was also adopted. These design dimensions are adopted based on the requirements of other specific applications and can be changed in practice. During the design process, it is assumed that the α-(poly-)Si layer uniformly covers the top surface and sidewalls of the waveguide. A 30nm thick Al2O3 bonding layer below the SiC film is used for bonding with the SiO2 lower cladding. The entire waveguide structure 110 is surrounded by the SiO2 cladding. In the numerical simulation of the design, standard material parameters of c-Si were used instead of standard material parameters of α-(poly-)Si.

[0098] Figure 3 Subfigures (a) and (b) in show the results of EME simulation of light transmission assuming a waveguide length of 1 mm, where subfigures (a) and (b) plot the IL versus Si cladding thickness for 1550 nm and 780 nm beams, respectively, with a filter length of 1 mm and TE / TM polarization mode. A smaller but increased IL is observed at a wavelength of 1550 nm due to the redistribution and confinement of the waveguide mode in the high refractive index Si layer. For a beam with a wavelength of 780 nm, the absorption depends on the degree of spatial overlap between the mode field and the Si layer 120. The modal overlap does not increase monotonically with the Si layer thickness t.

[0099] Figure 4 Sub-figures (a) to (d) of FIG. 1 plot simulated mode field amplitude distributions for TE and TM modes in wavelengths of 780 nm and 1550 nm within the first 10 μm of the waveguide 110 in the propagation direction for different values ​​of the thickness t of the Si layer 120 . Figure 2 The horizontal dashed line 290 shown in FIG. 2 represents the xy plane in which the mode field amplitude distribution is simulated. Figure 4 The results show that the 780 nm waveguide mode exhibits high-order mode interference when t reaches or exceeds 30 nm. This leads to different spatial overlaps, where the 780 nm light is periodically coupled into the Si film guided mode, such as Figure 4 Figure 3 shows the insets of sub-figures (a) and (b) of Figure 3. At t = 70 nm, interference occurs even in the TE and TM polarization modes at a wavelength of 1550 nm. Based on the simulation results, a 40 nm thick thin film α-Si layer was used in the device fabrication to achieve a significant target absorption loss of about 120 dB / mm at 780 nm light (pump light) while maintaining a negligible IL of less than 1 dB at 1550 nm light (signal light and idler light).

[0100] A.2. Manufacturing

[0101] The prototype LPF was Figure 5 The waveguide 110 is manufactured according to the manufacturing process shown in . A commercial 4-inch epitaxial 3C-SiC wafer on silicon is used in the manufacturing process. The thickness of the SiC film used to manufacture the waveguide 110 is 1.5 μm, and the film is chemically and mechanically polished. In the wafer-to-wafer bonding, a 4-inch Si substrate with a 3 μm thermal SiO2 layer is used, and the Si substrate is used as a carrier wafer. First, the two wafers are cleaned with a standard 120°C H2SO4 (98%): H2O2 (30%) = 10:1 solution. Then the two wafers are transferred to the Oxford ALD equipment to simultaneously deposit an Al2O3 layer with a thickness of 15 nm, so that after the bonding step, the total thickness of the Al2O3 layer is 30 nm. After deposition, the two wafers are contacted and pressed to start pre-bonding. Then, the pair of wafers is transferred to a Karl Suss SB6 bonder. The pre-bonded wafers are annealed at 300°C in vacuum for 3 hours to achieve permanent bonding. After the bonding step, a Si grinder was used to remove most of the Si substrate on the SiC side. The remaining Si substrate was removed with a tetramethylammonium hydroxide solution heated to 80°C. The remaining SiC film after removing the substrate was less than 50% of the original wafer. The remaining part was cut into small pieces, each measuring 1.2 cm x 1.2 cm.

[0102] The exposed SiC surface corresponds to the first layer of SiC epitaxially grown on the Si substrate. The first SiC layer has poor crystal quality due to the lattice mismatch between 3C-SiC and Si. Based on our numerical simulation results, a DRIE process with SF6 and O2 is recommended to thin the film to a target thickness of 460nm. A 500nm thick PECVD-fabricated SiO2 layer was deposited on the 3C-SiC film as a hard mask. The SiO2 hard mask was patterned using electron beam lithography and DRIE. The SiC film was then patterned using the same SF6 / O2 DRIE process. The selectivity of SiC to SiO2 was 1.45. The remaining SiO2 hard mask was subsequently removed by using a buffered oxide etchant. The sample was transferred to a CVD furnace to deposit a 40nm thick α-Si layer. The deposition temperature was maintained at 550°C to avoid partial crystallization of the α-Si film. After the α-Si deposition, photoresist was covered on the desired filter area using an i-line photolithography process. The α-Si layer in other places is completely removed by wet etching (Freckle etching solution). Then a 1000nm thick PECVD SiO2 upper cladding layer is deposited to protect the entire sample. Finally, the sample of the wafer is cut into columns for optical butt coupling. Butt coupling can easily achieve input / output coupling of various visible / NIR wavelengths.

[0103] Figure 6 Two images of the fabricated prototype LPF are shown. Figure 6 Sub-figure (a) is an image of the fabricated filter with different filter lengths, where the filter lengths range from 0 to 300 μm with a step size of 100 μm. Sub-figure (b) shows an SEM image of the waveguide to filter transition region. The transition region is designed to transition in an inclined manner with the aim of gradually adjusting the impedance mismatch between the waveguide region and the filter region. However, it should be noted that this inclined structure is not accurately transferred during wet etching, resulting in a rough inclined transition.

[0104] A.3. Experimental results

[0105] In the prototype LPF, a pair of long working distance objective lenses (numerical aperture of 0.42) are used for input / output butt coupling. The lens-to-lens normalized transmission spectra of TE and TM polarizations at different filter lengths were experimentally obtained. The corresponding experimental results are shown in Figure 7 as shown in .

[0106] Figure 7Subfigures (a) and (b) show the normalized transmission spectra of the fabricated filters with different lengths in the O, C, and L bands in TE and TM polarizations, where subfigures (a) and (b) show the results for TE polarization and TM polarization, respectively. The results show that the IL does not increase systematically as the filter length increases in steps of 100 μm, indicating that the passive waveguide losses in the transparent window are negligible in the length range considered. However, systematic differences are observed between the reference waveguide (i.e., the waveguide without any α-Si covering) and the three filters.

[0107] Figure 7 Subfigures (c) and (d) show the normalized transmission spectra for TE and TM polarizations at a wavelength of 780 nm (765-795 nm), respectively. Due to the use of straight waveguides in the filter, the background power caused by direct scattering of the input light is high, about 40 dB. It is observed that even for the shortest filter with a length of 100 μm, the transmitted light is at the background level of the scattered light. This observation is further confirmed by the near-field images of the output docking coupler captured by a charge-coupled device camera from the reference waveguide (especially the 100 μm long filter). The near-field images are respectively Figure 7 The exposure times for obtaining the near-field images are 1 ms and 200 ms for sub-figures (e) and (f), respectively, corresponding to an enhancement of 23 dB for the longer exposure. The transmitted light from the butt coupler after absorption is at the background level.

[0108] Figure 7 Subfigure (g) shows the wavelength-averaged transmission gain over three wavelength windows (1550 / 1310 / 780 nm) for TE and TM polarizations at different filter lengths. (Note that negative values ​​of the transmission gain mean power loss during transmission). Compared with the reference waveguide (i.e., the waveguide with a filter length of 0 μm), the ILs for the TE and TM polarization waveguide modes in the O-band were observed to be 0.8±1.0 dB and 1.9±0.5 dB, respectively, while the ILs for the TE and TM polarization waveguide modes in the C-band and L-band were 1.3±1.2 dB and 1.5±0.9 dB, respectively. For transmission at a wavelength of 780 nm, based on the characteristics of a 100 μm length filter, limited by the scattering of the input light, the lower limit ILs for the TE and TM polarization waveguide modes were estimated to be 230±8 dB / mm and 248±12 dB / mm, respectively. The extracted / estimated IL values ​​are significantly larger than the simulated values, which is mainly due to the fact that the material model adopted in the numerical simulation is based on standard c-Si, which is known to have a smaller absorption coefficient than that of α-Si adopted in the prototype LPF.

[0109] Figure 8Spectra measured using the OSA with and without 780nm pump light coupled into a 100μm long filter are shown. If 780nm light is coupled into the filter, a pump power of 1mW is used to obtain the measured spectrum. No significant optical power is observed to be generated by radiative recombination above or below the band gap energy corresponding to the photon energy of about 1100nm to 1550nm. The measured spectrum between about 800nm ​​and 1550nm is at the noise floor of the OSA. The results show that there is no significant re-emission of light above -90dB levels after absorbing a photon of 780nm light. This finding ensures that on-chip LPFs using indirect bandgap semiconductor absorbers do not act as secondary light sources. This finding is critical for the application of on-chip LPFs in quantum photonic circuits.

[0110] B. Details of Embodiments of the Present Disclosure

[0111] The embodiments of the present disclosure are developed as follows based on the details, examples, applications, experimental results, etc. of the prototype LPF disclosed above mainly in Part A, and are summarized and expanded where possible.

[0112] The first aspect of the present disclosure is to provide an optical LPF for long-pass filtering an incident light beam to produce a filtered light beam. The incident light beam includes a desired light component and an undesired light component. The desired light component has one or more first component wavelengths. The undesired light component has one or more second component wavelengths. Each wavelength in the one or more first component wavelengths is longer than each wavelength in the one or more second component wavelengths.

[0113] Reference Figure 1 As an illustrative example, the incident light beam 181 received by the prototype LPF 100 has a desired light component consisting of a signal light and an idler light and an undesired light component of a pump. The wavelengths of the signal light and the idler light are respectively longer than 1100 nm, while the wavelength of the pump light is less than 1100 nm.

[0114] By way of example, the following Fig. 9 describing the disclosed optical LPF, Fig. 9 A top view, a longitudinal cross-sectional view (A-A'), and a side cross-sectional view (BB') of an exemplary optical LPF 200 are shown.

[0115] like Fig. 9 As shown in , a three-dimensional rectangular coordinate system 80 is defined herein. In the coordinate system 80, the z direction is interpreted as referring to the vertical direction. In this specification and the appended claims, position and direction terms such as "above", "below", "higher", "upper", "lower", "top", "bottom" and "horizontal" are interpreted with reference to the z direction.

[0116] LPF 200 is arranged to receive incident light beam 281 and output filtered light beam 282. Incident light beam 281 includes desired light component 291 and undesired light component 292. Each of the constituent wavelengths of desired light component 291 is longer than each of the constituent wavelengths of undesired light component 292.

[0117] The LPF 200 includes a waveguide core 210 and a selective absorption layer 220 .

[0118] The waveguide core 210 corresponds to the waveguide structure 110 of the prototype LPF 100. The waveguide core 210 is used to receive an incident light beam 281, propagate a desired light component 291 and an undesired light component 292 inside the waveguide core 210, and output a filtered light beam 282.

[0119] A selective absorption layer 220 corresponding to the α-(poly-)Si layer 120 in the prototype LPF 100 is deposited on the waveguide core 210. The selective absorption layer 220 is used to selectively absorb the undesired light component 292 without attenuating the desired light component 291, or, when the desired light component 291 and the undesired light component 292 interact with the selective absorption layer 220 during propagation inside the waveguide core 210, the attenuation of the desired light component 291 by the selective absorption layer 220 is negligible compared to the absorption of the undesired light component 292. In particular, the selective absorption layer 220 is composed of an indirect bandgap semiconductor material, and the bandgap energy of the indirect bandgap semiconductor material is selected to be greater than the maximum photon energy associated with one or more first component wavelengths and less than the minimum photon energy associated with one or more second component wavelengths. This causes the selective absorption layer 220 to dissipate energy of the undesired light component 292 without dissipating the desired light component 291. Therefore, when the desired light component 291 and the undesired light component 292 interact with the selective absorption layer 220 during propagation in the waveguide core 210, the undesired light component 292 is attenuated, while the optical power of the desired light component 291 remains unchanged. Note that the maximum photon energy associated with the one or more first component wavelengths is calculated by: (1) calculating one or more photon energies corresponding to the one or more first component wavelengths; and (2) selecting the maximum value among the calculated one or more photon energies. The minimum photon energy associated with the one or more second component wavelengths is obtained by a similar method.

[0120] The indirect bandgap semiconductor material can be selected from α-Si or poly-Si. Generally, α-Si is preferred over poly-Si as an indirect bandgap semiconductor material because α-Si generally has better light absorption than poly-Si and can be deposited on a wafer at low cost through a simple deposition process.

[0121] In some embodiments, the thickness of the selective absorption layer 220 is less than or equal to 100 nm. As shown in the simulation results of the prototype LPF 100 in Part A, a thickness of 40 nm is sufficient for the α-Si layer 120 to achieve a high absorption loss of about 120 dB / mm for 780 nm light while maintaining a negligible IL of less than 1 dB for 1550 nm light.

[0122] In some embodiments, the waveguide core 210 is composed of SiC. The SiC material used as the waveguide core 210 may be 3C-SiC. Other materials that may be used to form the waveguide core 210 include LN and AlN.

[0123] Typically, the LPF 200 further includes an optical insulating layer 230 on which the waveguide core 210 is located. The optical insulator layer 230 provides a first reflective interface 211 between the waveguide core 210 and the optical insulator layer 230 to reflect the desired light component 291 during propagation of the desired light component 291 inside the waveguide core 210. Note that the first reflective interface 211 only needs to reflect the desired light component 291 and is not specifically designed to reflect the undesired light component 292, because the LPF 200 needs to ensure that the desired light component 291 is output from the LPF 200.

[0124] In some embodiments, the first reflective interface 211 is formed due to total internal reflection of the desired light component 291. Therefore, the respective materials forming the optical insulator layer 230 and the waveguide core 210 are selected to allow the desired light component 291 to be totally internally reflected at the first reflective interface 211. Therefore, the first refractive index of the waveguide core 210 is higher than the second refractive index of the optical insulator layer 230, wherein the first refractive index and the second refractive index are measured at each wavelength of the one or more first component wavelengths. In some embodiments, the optical insulator layer 230 is composed of SiO2.

[0125] Note that in the manufacture of the prototype LPF 100 as detailed above, a 30 nm thick Al2O3 bonding layer is placed below the SiC film (i.e., waveguide 110) for bonding with the SiO2 lower cladding. Since the desired light component of interest in the prototype LPF 100 has a component wavelength of approximately 1550 nm, the thickness of the bonding layer (30 nm) is much shorter than each wavelength of the light component. The SiO2 lower cladding plays a decisive role in achieving total internal reflection of the desired light component 291. Therefore, the SiO2 lower cladding is regarded as an optical insulator layer 230 that forms a first reflection interface 211 with the waveguide core 210.

[0126] In addition to relying on total internal reflection, the first reflective interface 211 may be created by directly using a reflective material (eg, gold) to form the optical insulator layer 230, wherein the reflective material is reflective at each of the one or more first component wavelengths.

[0127] exist Fig. 9 In the LPF 200 shown, the exposed areas of the waveguide core 210 and the selective absorption layer 220 are surrounded by air. Since the refractive index of air is almost 1 and lower than the corresponding refractive indexes of the waveguide core 210 and the selective absorption layer 220, a second reflection interface 212 similar to the first reflection interface 211 is generated for reflecting the desired light component 291 back to the waveguide core 210 by total internal reflection. Note that in most cases, the thickness of the selective absorption layer 220 is much shorter than each component wavelength of the desired light component 291. For example, the prototype LPF 100 is designed to have an α-Si layer with a thickness of 40nm, while the wavelength of the desired light component of interest in the prototype LPF 100 is about 1550nm. Therefore, the waveguide core 210 and the surrounding air play an important role in establishing the total internal reflection mechanism and generating the second reflection interface 212.

[0128] Figures 10A to 10D Some embodiments of LPF 200 are depicted in side cross-sectional view.

[0129] For reference, Fig. 10A A first LPF 300a is depicted, i.e., LPF 200 as described above, i.e., an exemplary embodiment of the disclosed optical LPF. Note that an air cladding, i.e., a cladding formed of air, is used in the first LPF 300a. In addition, the waveguide core 210 is a strip waveguide. A strip waveguide is basically a layer of strips confined between claddings. A rectangular waveguide is an example of a strip waveguide.

[0130] Fig. 10B A second LPF 300b is shown which is a variation of the first LPF 300a using a rib waveguide instead of a strip waveguide as the waveguide core 210. A rib waveguide is a waveguide in which the guiding layer is essentially a slab with one (or several) strips superimposed thereon.

[0131] Fig. 10CA third LPF 300c is shown, wherein the first LPF 300a further includes a cladding 240, which is deposited on a combination 270 consisting of at least the selective absorption layer 220 and the waveguide core 210. In addition to forming a protective layer for protecting the combination 270, the cladding 240 is also an optical insulator cladding, which provides a second reflection interface 212 between the waveguide core 210 and the cladding 240 to reflect the desired light component 291 during the propagation of the desired light component 291 inside the waveguide core 210. In some embodiments, the cladding 240 is composed of SiO2.

[0132] Fig. 10D A fourth LPF 300d is shown, which is formed from the first LPF 300a by: (1) using a rib waveguide instead of a strip waveguide as the waveguide core 210; and (2) including a cladding 240 deposited on a combination 270 consisting of at least the selective absorption layer 220 and the waveguide core 210.

[0133] Fig.11A and 11B A fifth LPF 400a and a sixth LPF 400b are shown as two further embodiments of the disclosed optical LPF. The fifth LPF 400a and the sixth LPF 400b differ in that the fifth LPF 400a has a straight waveguide core 210s, while the sixth LPF 400b has a curved waveguide core 210u. Therefore, the disclosed optical LPF has the flexibility of shaping the waveguide core 210 into a straight or curved waveguide core. As shown in the prototype LPF 100, this flexibility makes the footprint of the prototype LPF 100 compact.

[0134] Figures 12A to 12D Various waveguide-to-filter transition designs for the disclosed optical LPF are depicted. In particular, Fig. 12A An abrupt transition is shown; Fig. 12B The tilt transition is shown; Fig. 12C A first-order tapered transition is shown; Fig.12D A two-stage tapered transition is shown.Before describing the various transitions in detail, it is necessary to define several regions of the waveguide core.

[0135] The filtering section 520 of the waveguide core 210 is a first longitudinal section of the waveguide core 210 that is completely covered by the selective absorption layer 220a / b / c / d. The non-filtering section 510 of the waveguide core 210 is a second longitudinal section of the waveguide core 210 that is completely not covered by any selective absorption layer 220a / b / c / d. The transition region 515 of the waveguide core 210 is a third longitudinal section of the waveguide core 210 that is located between the non-filtering section 510 and the filtering section 520.

[0136] exist Fig. 12A The shape of the selective absorption layer 220a is such that the non-filtering section 510 abruptly transitions to the filtering section 520. Specifically, the longitudinal end of the selective absorption layer 220a has a profile 521a aligned with the cross section of the waveguide core 210.

[0137] exist Fig. 12B In the inclined transition shown, the longitudinal end of the selective absorption layer 220 b has an inclined profile 521 b covering the transition area 515 , so that the non-filtering section 510 gradually transitions into the filtering section 520 .

[0138] In such Fig. 12C In the primary tapered transition shown, the longitudinal end of the selective adsorption layer 220 c has a primary tapered profile 521 c covering the transition region 515 , so that the non-filtering section 510 gradually transitions into the filtering section 520 .

[0139] exist Fig.12D In the two-stage tapered transition shown, the longitudinal end of the selective adsorption layer 220 d has a two-stage tapered profile 521 d covering the transition region 515 , so that the non-filtering section 510 gradually transitions into the filtering section 520 .

[0140] and Fig. 12A Compared to the abrupt transition shown in Figures 12B to 12D The non-abrupt transition shown has the advantage of reducing the impedance mismatch between the non-filtering section 510 and the filtering section 520 .

[0141] A second aspect of the present disclosure is to provide a light conversion device for generating an output light beam from an input laser beam, wherein the light conversion device comprises any embodiment of the disclosed optical LPF.

[0142] The third aspect of the present disclosure is to provide an optical system, including any embodiment of the disclosed light conversion device. The disclosed optical system can be implemented as an integrated photonic chip. In addition, the optical system of the present disclosure can be applied to fields such as quantum communication and the Internet, quantum computers, quantum metrology and sensing.

[0143] With the help of Fig.13 The optical system and the light conversion device disclosed herein are exemplarily described. Fig.13 Schematic diagram of an exemplary embodiment of the disclosed optical system is shown. Fig.13 As shown, the optical system 1310 includes a light conversion device 1320 .

[0144] The optical conversion device 1320 is used to generate an output beam 1373 from an input laser beam 1370. The optical conversion device 1320 includes one or more nonlinear quantum light sources 1321 and an optical LPF 1322. The one or more nonlinear quantum light sources 1321 are collectively configured to perform SPDC on the input laser beam 1370 to nonlinearly generate a first beam 1372, so that the first beam 1372 includes a desired light component and an undesired light component. The desired light component has one or more first component wavelengths. The undesired light component has one or more second component wavelengths. Each wavelength of the one or more first component wavelengths is longer than each wavelength of the one or more second component wavelengths. The optical LPF 1322 is implemented as one of the embodiments of the disclosed optical LPF. The optical LPF 1322 is used to perform long-pass filtering on the first beam 1372 to generate an output beam 1373. The first beam 1372 defined for the optical conversion device 1320 is regarded as the incident beam 281 defined for the LPF 200. Similarly, the filtered beam 282 is regarded as the output beam 1373.

[0145] The optical system 1310 includes a light conversion device 1320 and one or more photonic circuits 1330. The one or more photonic circuits 1330 receive an output beam 1373 from the light conversion device 1320 and process the output beam 1373 to generate one or more optical signals 1375.

[0146] The generated one or more optical signals 1375 may be detected by single photon detection 1380 .

[0147] In fact, the optical system 1310 can be implemented as an integrated photonic chip. Similarly, the light conversion device 1320 can also be implemented on an integrated photonic chip.

[0148] C. Comparison with existing technologies

[0149] A review of the improvements of the present disclosure over the prior art is given below.Before the review, a review of the prior art disclosures considered is given.

[0150] Reference

[11] presents a wavelength filter based on cascaded microring resonators with high ER. In

[11] , a device was designed for TE polarization, and on-chip microheaters were used to align each microring element to the desired wavelength. The maximum filtering bandwidth achieved was 125 GHz. However, the technique of

[11] requires precise control of ten microheaters to tune the microring elements, thus increasing energy consumption. The filtering bandwidth is limited to 125 GHz around the target wavelength. This is not convenient for applications that require flexibility in the wavelength of the pump light, such as SPDC-based photon sources. This technique is only applicable to the designed TE polarization propagation. Taking into account the polarization-dependent microring resonances, another design is required for filtering of TM polarization.

[0151] Reference

[12] presents a standard reflector based on a Bragg grating for a target pump wavelength with a target ER of 100 dB. The technique of

[12] requires a grating period of 320 nm and a length of 2.576 mm. However, the filtering bandwidth presented in

[12] is very narrow (<0.01 nm) and fixed at the target wavelength. This technique cannot be applied to applications that require tuning of the pump wavelength (e.g., SPDC-based photon sources). This technique requires precise fabrication of the grating.

[0152] Reference

[13] demonstrated an ER of 56 dB using 4-stage cascaded UMZIs. The ER can be further improved by cascading more than 4 stages. The demonstrated filtering bandwidth exceeds 1 nm. This technique requires precise fabrication of the cascaded UMZIs to achieve the required spectral overlap between the single-stage filter bands and does not involve active wavelength alignment. For applications that require wide bandwidth to suppress short wavelength (pump) light (e.g., SPDC-based photon sources), the filtering bandwidth of this technique is still limited.

[0153] Reference

[14] presents a filter based on a cascaded 16-stage grating-assisted reverse coupler. This technique achieves an ER of 68.5 dB and a filtering bandwidth of 3 nm. This technique combines grating and directional coupler filtering. The grating features a period of 244 nm and a duty cycle of 50%. The total length of the device is 2 mm. However, the filtering bandwidth of this technique is still limited to the central wavelength, making it inconvenient for applications that require flexible selection of pump light wavelengths (e.g., SPDC-based and color center-based quantum light sources). The 244 nm grating period used in this technique requires advanced device manufacturing equipment.

[0154] Reference

[15] achieved 70 dB attenuation at wavelengths near 775 nm and an IL of 3 dB at 1550 nm by using a filter based on cascaded tapered directional couplers. This technology has a filter bandwidth of 16 nm near 775 nm and a passband bandwidth of 50 nm at 1550 nm. However, the filter bandwidth used by this technology is still limited. The IL increases with the number of cascaded filter stages. It can be expected that a total ER of more than 100 dB will result in an IL of more than 3 dB at a wavelength of 1550 nm, which will result in a reduction of more than 6 dB in photon pair counts.

[0155] Compared to the techniques disclosed in

[11] -

[15] mentioned above, the present disclosure achieves a significantly wider filtering band for short-wavelength pump light and a passband for long-wavelength generated light based on the intrinsic absorption of deposited thin-film silicon. The suppression band naturally covers the typical pump light wavelengths of 532, 650, 780 and 900 nm selected in the literature for various on-chip photon sources, while the passband spans the telecommunication bands of about 1.31 μm and 1.55 μm.

[0156] Compared to all the above mentioned techniques, the optical LPF disclosed herein is simple in concept and does not require advanced manufacturing equipment. The main design parameter of the LPF 200 is the thickness of the absorbing thin film layer.

[0157] Compared with all the above-mentioned techniques, the optical LPF disclosed in this article occupies much less space on the chip because the total length of the filter structure is less than 1 mm and the waveguide filter can be bent into a compact shape.

[0158] References

[0159] The following is a list of references occasionally cited in this specification. The entire disclosure of each of these references is incorporated herein by reference.

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[10] A.Al Sayem,R.Cheng,S.Wang,and H.X.Tang,“Lithium-niobate-on-insulator waveguide-integrated superconducting nanowire single-photondetectors,”Appl.Phys.Lett.116,(2020).

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Claims

1. An optical long-pass filter, the optical long-pass filter is used to perform long-pass filtering on an incident light beam to produce a filtered light beam, the incident light beam comprises a desired light component and an undesired light component, the desired light component has one or more first component wavelengths, the undesired light component has one or more second component wavelengths, each wavelength of the one or more first component wavelengths is longer than each wavelength of the one or more second component wavelengths, the filter comprising: a waveguide core, the waveguide core being configured to receive the incident light beam, propagate the desired light component and the undesired light component inside the waveguide core, and output the filtered light beam; as well as a selective absorption layer deposited on the waveguide core, the selective absorption layer being composed of an indirect bandgap semiconductor material selected to have a bandgap energy greater than a maximum photon energy associated with the one or more first component wavelengths and less than a minimum photon energy associated with the one or more second component wavelengths, such that when the desired light component and the undesired light component interact with the selective absorption layer during propagation within the waveguide core, the undesired light component is attenuated while the optical power of the desired light component is preserved.

2. The filter according to claim 1, wherein The indirect bandgap semiconductor material is selected to be amorphous silicon (α-Si) or polycrystalline silicon (poly-Si).

3. The filter according to claim 2, wherein: The thickness of the selective absorption layer is less than or equal to 100 nm.

4. The filter according to claim 1, wherein The waveguide core is realized in the form of a strip waveguide.

5. The filter according to claim 1, wherein The waveguide core is realized in the form of a rib waveguide.

6. The filter according to claim 1, wherein The waveguide core is composed of cubic silicon carbide (3C-SiC).

7. The filter according to claim 1, wherein: The waveguide core is composed of a material selected from the group consisting of silicon carbide (SiC), lithium niobate (LN) and aluminum nitride (AlN).

8. The filter according to claim 1, further comprising: An optical insulator layer on which the waveguide core is located, wherein the optical insulator layer provides a first reflective interface between the waveguide core and the optical insulator layer to reflect the desired light component during propagation of the desired light component inside the waveguide core.

9. The filter according to claim 8, wherein: The optical insulator layer is composed of silicon dioxide (SiO2).

10. The filter according to claim 8, wherein: The respective materials forming the optical insulator layer and the waveguide core are selected to allow total internal reflection of the desired light component at the first reflective interface.

11. The filter according to claim 8, further comprising: a cladding layer deposited on a combination of at least the selective absorption layer and the waveguide core, wherein the cladding layer is an optical insulator cladding layer providing a second reflection interface between the waveguide core and the optical insulator cladding layer to reflect the desired light component during propagation of the desired light component inside the waveguide core.

12. The filter according to claim 11, wherein The cladding is composed of silicon dioxide (SiO2).

13. The filter according to claim 1, wherein: The waveguide core is shaped to be straight.

14. The filter according to claim 1, wherein The waveguide core is shaped to be curved.

15. The filter of claim 1, wherein: The selective absorption layer is shaped so that a non-filtering section of the waveguide core transitions abruptly to a filtering section thereof; The filtering section is a first longitudinal section of the waveguide core, the first longitudinal section being completely covered by the selective absorption layer; and The non-filtering section is a second longitudinal section of the waveguide core which is completely not covered by any selectively absorbing layer.

16. The filter of claim 1, wherein: The longitudinal end of the selective absorption layer has an inclined profile, and the inclined profile covers the transition area between the non-filtering section and the filtering section of the waveguide core, so that the non-filtering section gradually transitions to the filtering section; The filtering section is a first longitudinal section of the waveguide core, the first longitudinal section being completely covered by the selective absorption layer; as well as The non-filtering section is a second longitudinal section of the waveguide core which is completely not covered by any selectively absorbing layer.

17. The filter of claim 1, wherein: The longitudinal end of the selective absorption layer has a primary tapered profile, and the primary tapered profile covers a transition region between a non-filtering section and a filtering section of the waveguide core, so that the non-filtering section gradually transitions to the filtering section; The filtering section is a first longitudinal section of the waveguide core, the first longitudinal section being completely covered by the selective absorption layer; as well as The non-filtering section is a second longitudinal section of the waveguide core which is completely not covered by any selectively absorbing layer.

18. The filter of claim 1, wherein: The longitudinal end of the selective absorption layer has a two-stage tapered profile, and the two-stage tapered profile covers the transition area between the non-filtering section and the filtering section of the waveguide core, so that the non-filtering section gradually transitions to the filtering section; The filtering section is a first longitudinal section of the waveguide core, the first longitudinal section being completely covered by the selective absorption layer; as well as The non-filtering section is a second longitudinal section of the waveguide core which is completely not covered by any selectively absorbing layer.

19. A light conversion device for generating an output light beam from an input laser beam, comprising: one or more nonlinear quantum light sources, the one or more nonlinear quantum light sources being collectively configured to perform spontaneous parametric down-conversion on the input laser beam to nonlinearly generate a first light beam, such that the first light beam includes a desired light component and an undesired light component, the desired light component having one or more first component wavelengths, the undesired light component having one or more second component wavelengths, each of the one or more first component wavelengths being longer than each of the one or more second component wavelengths; as well as The optical long-pass filter according to claim 1, wherein the optical long-pass filter is used to perform long-pass filtering on the first light beam to generate an output light beam, wherein the first light beam is regarded as the incident light beam and the filtered light beam is regarded as the output light beam.

20. An optical system comprising: The light conversion device according to claim 19; as well as One or more photonic circuits for processing the output light beam.

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