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EP-4738365-A1 - ABSORPTIVE PHOTONIC MEMORY

EP4738365A1EP 4738365 A1EP4738365 A1EP 4738365A1EP-4738365-A1

Abstract

An absorptive photonic memory comprises absorptive-photonic-memory material, two single-mode ports respectively arranged to receive and transmit memory light to be absorbed by, stored in and emitted from said absorptive-photonic-memory material, and control light that controls said absorptive-photonic-memory material, a multi-mode port connected to the absorptive-photonic-memory material and a spatial multiplexer that spatially multiplexes the two single-mode ports towards the multi-mode port, said spatial multiplexer comprising a plurality of waveguides in a photonic lantern configuration wherein a first subset of the plurality of waveguides is configured to guide the memory light and a second subset of the plurality of waveguides is configured to guide the control light and at least one passive or active optical circuit.

Inventors

  • The designation of the inventor has not yet been filed

Assignees

  • Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk Onderzoek TNO

Dates

Publication Date
20260506
Application Date
20241030

Claims (15)

  1. An absorptive photonic memory (100; 200; 300) comprising: - An absorptive-photonic-memory material (102); - Two single-mode ports (104) respectively arranged to receive and transmit memory light to be absorbed by, stored in and emitted from said absorptive-photonic-memory material (102), and control light that controls said absorptive-photonic-memory material (102) to prepare the absorptive-photonic-memory material, and to control the writing, storage and reading of said memory light; - A multi-mode port (106) connected to the absorptive-photonic-memory material (102); and - A spatial multiplexer (108) that spatially multiplexes the two single-mode ports (104) towards the multi-mode port (106), said spatial multiplexer comprising: ∘ a plurality of waveguides (110) in a photonic lantern configuration wherein a first subset of the plurality of waveguides (110a) is configured to guide the memory light and a second subset of the plurality of waveguides (110b) is configured to guide the control light; and ∘ passive or active optical circuits connecting one of the two single-mode ports (104a) to the first subset of the plurality of waveguides (110a) and the other one of the two single-mode ports (104b) to the second subset of the plurality of waveguides (110b), said optical circuits comprising at least one beam splitter (112).
  2. The absorptive photonic memory (100; 200; 300) according to claim 1, further comprising a cavity comprising the absorptive-photonic-memory material (102), said cavity comprising of fully and/or partially reflecting surfaces that surround said absorptive-photonic-memory material.
  3. The absorptive photonic memory (100; 200; 300) according to claim 2, wherein reflectivity of a mirror located at an end of the cavity connecting with the spatial multiplexer (108) is such that there is impedance matching with the absorptive-photonic-memory material.
  4. The absorptive photonic memory (100; 200; 300) according to any of the preceding claims, wherein the control light is arranged to perform spectral hole burning on the absorptive-photonic-memory material (102).
  5. The absorptive photonic memory (100; 200; 300) according to any of the preceding claims, wherein at least one of the two single-mode ports (104) comprises an optical fiber.
  6. The absorptive photonic memory (100; 200; 300) according to claim 1, wherein the one of the two single-mode ports (104b) arranged to receive control light comprises an optical fiber coupled to the second subset of the plurality of waveguides (110b) using at least one of a butt joint, a grating, and a flip-chip arrangement and/or the other one of the two single-mode ports (104a) comprises another optical fiber coupled to the first subset of the plurality of waveguides (110a) using another at least one of a butt joint, a grating, and a flip-chip arrangement.
  7. The absorptive photonic memory (100; 200; 300) according to any of the preceding claims, wherein at least one of the first subset of the plurality of waveguides (110a) comprises a curved section or a mirror to guide the memory light.
  8. The absorptive photonic memory (200) according to any of the preceding claims, further comprising a third single-mode port configured to receive memory light and wherein the first subset of the plurality of waveguides (110a) comprises two waveguides respectively coupled to the one of the two single-mode ports (104a-i) arranged to receive and transmit memory light and to the third single-mode port (104a-ii), wherein the two waveguides are connected at a middle section by an optical coupler.
  9. The absorptive photonic memory (300) according to any of claims 1-7, further comprising a third single-mode port configured to receive memory light and wherein the first subset of the plurality of waveguides (110a) comprises at least two waveguides respectively coupled to the one of the two single-mode ports arranged to receive and transmit memory light and to the third single-mode port, wherein the two waveguides are connected at a middle section by an optical coupler and wherein the memory light guided by one of the two waveguides is 90 degree phase shifted with respect to the memory light guided by the other of the two waveguides.
  10. The absorptive photonic memory (300) according to claim 9, wherein the one of the two waveguides is quarter a wavelength of the memory light longer than the other of the two waveguides or comprises another type of 90-degree phase shifter.
  11. The absorptive photonic memory (300) according to any of claims 7-8 wherein one of the single-mode ports matches a first order mode in the absorptive-photonic-memory material (102) and another single-mode port matches a fundamental order mode in the absorptive-photonic-memory material (102).
  12. The absorptive photonic memory (100; 200; 300) according to any of the preceding claims, further arranged in a photonic integrated circuit.
  13. The absorptive photonic memory (100; 200; 300) according to any of the preceding claims, further arranged in a 3-dimensional configuration.
  14. A method for using the absorptive photonic memory (100; 200; 300) according to any of claims 1-13.
  15. A method of manufacturing the absorptive photonic memory (100; 200; 300) according to any of claims 1-13.

Description

FIELD OF THE INVENTION The invention relates to an absorptive photonic memory and related method of manufacturing and using the absorptive photonic memory. BACKGROUND OF THE INVENTION Photonic memories are used as quantum memories in, for instance, quantum-communication systems for quantum-entanglement distribution. Such systems use quantum repeaters to teleport quantum states over larger distances. Additional to entangled photon-pair sources and Bell-state measurements, such quantum-repeater systems need quantum memories to operate. The Atomic Frequency Comb (AFC) protocol is a promising approach to create photonic memories, e.g. for use as quantum memory in a quantum-repeater system. An example of this can be found in "Multimode capacity of atomic-frequency comb" by Ortu et all. AFC protocols use a specially manufactured crystal with rare-earth doping to achieve large static inhomogeneous broadening, narrow homogeneous broadening and low spectral diffusion. The AFC protocol has several phases: In the preparation phase, some high intensity light with finely-tailored spectral, intensity and timing properties is used to prepare the crystal through spectral hole burning, in order to achieve a spectrally finely-tuned combination of atomic states ("ground", "excited", "shelf", ...).In the write phase, a photonic pulse is absorbed by the AFC, and in this way it is "written" into the crystal. When used as a quantum memory, single-photon pulses are used. These single photons would typically have a quantum state that is entangled with another photon at another location, e.g. through generation by an entangled photon-pair source.In the read phase, the photonic pulse is retrieved. In case of the single photon, the emitted photon has the same quantum state as the absorbed one, and it has retained entanglement with the other photon at the other location. There are many variations to the AFC protocol, each with its own technological complexity and features. In many cases, the time between write and read is already determined at the preparation phase, as the storage time is determined by the spectral properties of the preparation light. Also, "random-access" AFC implementations are known with long storage time, see for instance "One-hour coherent optical storage in an atomic frequency comb memory" by Ma et al. The use of a cavity is a known feature for an AFC, see e.g. "Towards a Realistic Model for Cavity-Enhanced Atomic Frequency Comb Quantum Memories" by Taherizadegan et al. A cavity is built from fully and/or partially reflective surfaces (mirrors) that surround absorptive-photonic-memory material. The use of a cavity enhances the storage efficiency, if proper impedance matching is applied. That is, the optical length of the cavity should match with the frequency of the stored photon(s), and the reflectivity of the "mirrors" at the cavity ends should match with the absorption by the crystal, to minimize photon(s) bouncing out of the cavity instead of getting absorbed in the write phase. In the read phase, the re-emitted photon may come out at the same side as where the to-be-absorbed photon entered. SUMMARY OF THE INVENTION According to a first aspect of the invention, it is provided an absorptive photonic memory comprising: An absorptive-photonic-memory material;Two single-mode ports respectively arranged to receive and transmit memory light to be absorbed by, stored in and emitted from said absorptive-photonic-memory material, and control light that controls said absorptive-photonic-memory material to prepare the absorptive-photonic-memory material, and to control the writing, storage and reading of said memory light;A multi-mode port connected to the absorptive-photonic-memory material; andA spatial multiplexer that spatially multiplexes the two single-mode ports towards the multi-mode port, said spatial multiplexer comprising a plurality of waveguides in a photonic lantern configuration wherein a first subset of the plurality of waveguides is configured to guide the memory light and a second subset of the plurality of waveguides is configured to guide the control light and at least one passive or active optical circuit connecting one of the two single-mode ports to the first subset of the plurality of waveguides and/or the other one of the two single-mode ports to the second subset of the plurality of waveguides, the at least one passive or active optical circuit comprising at least one beam splitter. This allows to spatially multiplex the memory light and the control light using the spatial multiplexer. By spatial multiplexing using a photonic lantern configuration a compact and light weight absorptive photonic memory is provided. This might be especially relevant in satellite systems. State-of-the-art systems comprise much bigger bulk components, like beam splitters or optical switches in combination with time multiplexing between the control and the memory light. Also, the disclosed absorptive photonic memory