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US-20260126676-A1 - PHOTONIC FILTER

US20260126676A1US 20260126676 A1US20260126676 A1US 20260126676A1US-20260126676-A1

Abstract

A microwave photonic filter, MWP filter, for bandpass filtering. The MWP filter includes a distributed feedback resonator structure comprising a first resonant cavity and a second resonant cavity, wherein the distributed feedback resonator structure is configured such that an input optical signal is filtered by the first resonant cavity and second resonant cavity to generate a filtered output optical signal. The MWP filter further includes a first micro heater configured to adjust the temperature of the first resonant cavity and a second micro heater configured to adjust the temperature of the second resonant cavity. The MWP filter further includes at least one of: a general heater configured to adjust the temperature of the distributed feedback resonator structure; and a tuneable continuous wave laser source, wherein the MWP filter is configured to tune a wavelength of light generated by the tuneable continuous wave laser source and used by the MWP filter.

Inventors

  • Claudio Porzi
  • Antonella Bogoni
  • Fabio Cavaliere

Assignees

  • TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Dates

Publication Date
20260507
Application Date
20231002

Claims (20)

  1. 1 . A microwave photonic filter, MWP filter, for bandpass filtering, the MWP filter comprising: a distributed feedback resonator structure comprising a first resonant cavity and a second resonant cavity, the distributed feedback resonator structure being configured such that an input optical signal is filtered by the first resonant cavity and second resonant cavity to generate a filtered output optical signal; a first micro heater configured to adjust the temperature of the first resonant cavity; a second micro heater configured to adjust the temperature of the second resonant cavity; and at least one of: a general heater configured to adjust the temperature of the distributed feedback resonator structure; and a tuneable continuous wave laser source, wherein the MWP filter is configured to tune a wavelength of light generated by the tuneable continuous wave laser source and used by the MWP filter.
  2. 2 . The MWP filter of claim 1 , wherein the first resonant cavity and second resonant cavity are embedded between Bragg grating mirrors.
  3. 3 . The MWP filter of claim 1 , wherein the MWP filter is formed as a silicon-on-insulator photonic integrated circuit, or wherein the MWP filter is formed as a lithium niobate on insulator integrated circuit.
  4. 4 . The MWP filter of claim 3 , wherein the first micro heater and second micro heater are formed as resistive structures, and have separate input voltages from one another.
  5. 5 . The MWP filter of claim 1 , further comprising at least one further resonant cavity and corresponding further micro heater.
  6. 6 . The MWP filter of claim 5 , wherein the at least one further resonant cavity is positioned in series with the first resonant cavity and the second resonant cavity.
  7. 7 . The MWP filter of claim 1 , wherein the MWP filter bandwidth is programmable in a range between 500 MHz and 3 GHz.
  8. 8 . The MWP filter of claim 1 , further comprising: an optical splitter; an electro-optical phase modulator; an optical coupler; and a photodiode; and wherein the MWP filter is configured such that: an incident signal from a tuneable continuous wave laser source is split by the optical splitter to form first and second laser portions; the first laser portion is phase modulated by the electro-optical phase modulator based on a received radio frequency, RF, signal, then filtered by the distributed feedback resonator structure to generate a sideband signal; the sideband signal and second laser portion are recombined at the optical coupler to generate a composite signal; and the composite signal is converted to a filtered RF signal at the photodiode.
  9. 9 . The MWP filter of claim 8 , wherein the MWP filter is configured to tune the tuneable continuous wave laser with reference to the temperature adjustments provided by the first micro heater and a second micro heater.
  10. 10 . The MWP filter of claim 9 , wherein the RF signal is an Intermediate Frequency, IF, signal.
  11. 11 . A photonic integrated RF receiver comprising microwave photonic filter, the MWP filter comprising: a distributed feedback resonator structure comprising a first resonant cavity and a second resonant cavity, the distributed feedback resonator structure being configured such that an input optical signal is filtered by the first resonant cavity and second resonant cavity to generate a filtered output optical signal; a first micro heater configured to adjust the temperature of the first resonant cavity; a second micro heater configured to adjust the temperature of the second resonant cavity; and at least one of: a general heater configured to adjust the temperature of the distributed feedback resonator structure; and a tuneable continuous wave laser source, wherein the MWP filter is configured to tune a wavelength of light generated by the tuneable continuous wave laser source and used by the MWP filter.
  12. 12 . The photonic integrated RF receiver of claim 11 , wherein the photonic integrated RF receiver is comprised in a radio network node.
  13. 13 . A method for bandpass filtering using a microwave photonic, MWP, filter, the method comprising: tuning a bandwidth of the MWP filter by adjusting the temperature of a first resonant cavity of a distributed feedback resonator structure using a first micro heater, and adjusting the temperature of a second resonant cavity of the distributed feedback resonator structure using a second micro heater; tuning the central frequency of the MWP filter by at least one of: adjusting the temperature of the distributed feedback resonator structure using a general heater; and tuning a wavelength of light generated by a tuneable continuous wave laser source and used by the MWP filter; and filtering an optical signal using the tuned MWP filter.
  14. 14 . A method according to claim 13 , further comprising: receiving a radio frequency, RF, signal, and upconverting the RF signal into an optical signal; and filtering the optical signal used the tuned MWP filter.
  15. 15 . The MWP filter of claim 2 , wherein the MWP filter is formed as a silicon-on-insulator photonic integrated circuit, or wherein the MWP filter is formed as a lithium niobate on insulator integrated circuit.
  16. 16 . The MWP filter of claim 15 , wherein the first micro heater and second micro heater are formed as resistive structures, and have separate input voltages from one another.
  17. 17 . The MWP filter of claim 2 , further comprising at least one further resonant cavity and corresponding further micro heater.
  18. 18 . The MWP filter of claim 17 , wherein the at least one further resonant cavity is positioned in series with the first resonant cavity and the second resonant cavity.
  19. 19 . The MWP filter of claim 2 , wherein the MWP filter bandwidth is programmable in a range between 500 MHz and 3 GHZ.
  20. 20 . The MWP filter of claim 2 , further comprising: an optical splitter; an electro-optical phase modulator; an optical coupler; and a photodiode; and wherein the MWP filter is configured such that: an incident signal from a tuneable continuous wave laser source is split by the optical splitter to form first and second laser portions; the first laser portion is phase modulated by the electro-optical phase modulator based on a received radio frequency, RF, signal, then filtered by the distributed feedback resonator structure to generate a sideband signal; the sideband signal and second laser portion are recombined at the optical coupler to generate a composite signal; and the composite signal is converted to a filtered RF signal at the photodiode.

Description

TECHNICAL FIELD Embodiments described herein relate to a photonic filter, in particular a microwave photonic (MWP) filter for passband filtering, a photonic integrated radio frequency (RF) receiver, a radio network node and method for use of the same. BACKGROUND Modern electronic systems utilising transmission and reception, such as mobile and satellite wireless communications and radar sensor systems, typically operate over multiple bands, covering a wide range of frequencies extending from few GHz up to the millimeter-wave and sub-THz bands. As the carrier frequency increases, larger bandwidth is available for high-throughput and low-latency services, with single channel bandwidth that can be as wide as hundreds of megahertz, as in the Frequency Range two (FR2) of 3rd Generation Partnership Project (3GPP) 5th Generation (5G) New Radio (NR) standard, or even few GHz as in the Institute of Electrical and Electronic Engineers (IEEE) 802.11ad standard for networks operating at 60 GHZ (available at https://www.techstreet.com/ieee/standards/ieee-802-11ad-2012?product_id=1820568 as of 27 Sept. 2022). Ultra-wideband antennas, covering bandwidths as large has 100 GHz are also available. In this context, widely tunable and bandwidth reconfigurable RF bandpass filters are desirable for enhancing flexibility of wideband receivers. Standard Radio Frequency (RF) filtering techniques based on coupled resonators typically provide limited tuning of the filter's central frequency and bandwidth. Accordingly, digitally-switched filter banks are typically used for increasing the range of covered bands. Microwave photonic (MWP) filters, in which the RF signal is upconverted to an optical signal and processed in the optical domain can overcome this limitation, thanks to the ultra-wide band availability at optical frequencies and the large reconfiguration capability of optical systems. These features make MWP filters promising candidates for performing wideband analog front-end processors, allowing the use of filters banks and/or high-speed analog-to-digital converters to be avoided. To practically deploy MWP filtering approaches in real systems, photonic integration provides the key advantages of reduced size, weight, and power consumption, an improved stability, and the possibility of reducing per unit fabrication costs through high-volume production. However, existing MWP bandpass filters have presented limited performance and/or a low integration levels. Discrete-element RF filters may provide high precision and small size, but typically only allow operation up to about 10 GHz, limited by the availability and tolerance of components with small capacitance and inductance values and moderate dissipative losses. Waveguide cavity filters may facilitate higher frequency values, at the expense of dimensions, weight, and costs, an issue that can be alleviated using ceramic-loaded resonators. However, tuning of the central frequency is constrained to within the specific designed band of operation, and bandwidth reconfigurability is typically limited to few percent of the filter's nominal central frequency. Planar filters, typically realized with microstrip topology, offer the most compact layout, and may be tuned and reconfigured using either analog or digital control signals, but are most suitable for low-to-mid frequency applications due to large losses at high frequencies. The central frequency tunability of planar filters may be improved through the use of filter banks and switches, with tuning resolution limited by the number of control digits. Although this approach allows also for reconfiguring the filter bandwidth, the allowed bandwidth tuning range of few hundreds of MHz makes this approach more suitable for programmable Intermediate Filtering (IF) filtering. Photonics-based processing of microwave signals has highlighted the possibility of broadband tuning and reconfigurable operation. Existing photonic integrated solutions typically concentrate on implementing the optical core processor (typically, a photonic integrated filter) in waveguide technology, while leveraging on additional bulk optics components for complete system demonstration. For instance, up-conversion to the optical domain of the RF signal to be processed is typically performed using external electro-optic (EO) modulators, either because the performance of photonic integrated devices is not yet as mature as that of commercial devices, or because high-speed EO effect is not supported by the platform providing the high-performing integrated optical filter processor. The bandwidth reconfigurability of MWP filters based on photonic integrated frequency comb sources may be realized through expensive equipment in liquid crystal on silicon technology; this may hinder cost-effective utilization of the device in practical applications. Frequency tuning and bandwidth reconfigurability of a bandpass optical filter (OF) realized in III-V semiconductor (InP) technology