FIELD

An electro-optical receiver monolithically integrated with photonic integrated circuits is provided.

BACKGROUND

Microwave radiometers (MRs) are sensitive receivers that measure small changes in the radiated power emanating naturally from the Earth's surface and atmosphere (i.e. blackbody radiation). Space-based MRs are important for atmospheric sounding (vertical profiling) and Earth surface imaging measurements necessary for generating a wide range of geophysical quantities. Sounding is the process where multi-frequency observations provide measurements at different altitudes to retrieve an altitude profile of a specific characteristic of the atmosphere. For example, retrievals of atmospheric temperature and humidity profiles are obtained routinely from space-based MRs using channels near the 60 GHz oxygen and 183 GHz water absorption features respectively.

Proven algorithms derive physical quantities from the raw power measurements made by a MR (e.g. atmospheric temperature, humidity, precipitation, wind vectors, sea surface temperature, etc.), which in turn feed weather and climate models. Conventional MRs include an antenna and a bandpass filter that selects the received input spectrum. The filtered input is amplified by a low noise amplifier (LNA), and mixed with a local oscillator to down-convert the signal to an intermediate frequency band (in some designs the bandpass filter is placed after the amplifier to improve measurement sensitivity). The resulting intermediate frequency signals are filtered into individual channels prior to detection, integration and analog to digital conversion. In conventional instruments, the size and weight of the MR electronics are driven in part by the dimensions of the filter banks required to enable multichannel operation, which are proportional to wavelength (typically in the centimeter to multi-millimeter microwave range). As a result, providing a MR capable of many channel operation is a particular challenge. Moreover, these constraints make the provision of hyperspectral sensors, which measure energy simultaneously in numerous channels over multiple frequency bands, providing a measurement capability that extends across a broad spectral range, at best impractical. In particular, while hyperspectral capabilities have been available in optical instruments, they have been unavailable in microwave instruments, due in part to the design complexity, size, weight, power and large quantities of components required to implement those capabilities at microwave frequencies.

In addition to the long-standing barriers to providing multiple channel operation in a practical instrument, the trend towards smaller, lower-cost spacecraft has made the design of a practical MR even more of a challenge. For example, mission cost reduction pressure is driving the re-evaluation of the entire weather observation architecture, and has resulted in the increased use of lower-cost spacecraft (e.g. CubeSats and SmallSats), which are being exploited individually and in constellations. These small-size options can only compete with the traditional large, more expensive systems, when sensors that meet small spacecraft integration volume constraints provide comparable or improved performance. Therefore, to fully realize the observation potential of the small platforms, sensor payloads, including MRs, must evolve to smaller cost, size, weight and power, while delivering the required performance.

SUMMARY

Microwave photonics provide a means to realize hyperspectral measurement capability at microwave frequencies within a small instrument volume. In a microwave photonic based radiometer, the microwave signal is converted into the optical domain to enable processing of the signal optically. Specifically, an electro-optical modulator modulates the incoming microwave signal onto a carrier provided by a pump laser. This process creates optical sidebands equally spaced from the laser carrier (e.g. a common telecom wavelength of 1550 nm, approximately 194 THz) by the modulating radio frequency center frequency (e.g. in the range of approximately 20-200 GHz). Each sideband contains the entire microwave input spectrum. Once in the optical domain, the microwave signals are processed with components fabricated into photonic integrated circuits (PICs) that are extremely small (compared to conventional microwave components), low loss, wideband, and immune to the effects of radio frequency interference.

Embodiments of the present disclosure provide a MR that includes an electro-optical receiver incorporating an electro-optic modulator that operates to up-convert received radio frequency (RF) signals to the optical domain. In addition, the electro-optic receiver features a number of components that are provided on a single silicon substrate. More particularly, in at least some embodiments, an electro-optical receiver is provided that includes photonic components that are monolithically integrated on a common silicon substrate. In accordance with still other embodiments, photonic components and electronics components are monolithically integrated on a common substrate.

Methods in accordance with embodiments of the present disclosure include receiving a radio frequency signal or signals at an antenna and band-pass filtering those signals. The filtered signals can then be amplified by a LNA. Next, the signals are up-converted to optical frequencies in an electro-optic modulator, which receives a carrier signal from a pump laser. The upconverted signals can then be filtered by an optical filter, and converted to an electrical signal using a photodetector. The electrical signal produced by the photodetector can then be amplified, integrated, and digitized by an amplifier, an integrator, and an analog to digital converter respectively. In accordance with embodiments of the present disclosure, the photonic components, such as the electro-optic modulator, the pump-laser, the optical filter, and the photodetector, are all implemented monolithically on a single silicon substrate. In accordance with further embodiments of the present disclosure, the electronic components, such as the amplifiers, the integrator, and the analog to digital converter, are also implemented monolithically on the single silicon substrate, together with the photonic components.

In at least some embodiments of the present disclosure, an electro-optic receiver that includes multiple channels can be provided. The multiple channels are defined by the optical filter, and each channel can be associated with a photodetector. In accordance with at least some further embodiments of the present disclosure, the electro-optic receiver can provide at least 50 channels. In accordance with still other embodiments, the electro-optic receiver can provide more than 100 channels.

Additional features and advantages of embodiments of the present disclosure will become more readily apparent from the following discussion, particularly when taken together with the accompanying drawings.

