Definition of an Oscillator

An oscillator is a device that can convert direct current (DC) power into alternating current (AC) power without the need for an external signal. It includes a process and function that transitions from non-oscillating to oscillating, and can complete the conversion of DC power to AC power. Such a device can be called an "oscillator".

Definition of an Optoelectronic Oscillator

An optoelectronic oscillator (OEO) is generally a microwave photonic self-oscillating system composed of a light source, an intensity modulator, a filter, and a photodetector (PD) with a positive feedback optoelectronic mixing loop. It uses the modulator and the low-loss characteristics of optical fibers to convert continuous light into a stable, spectrally clean RF/microwave signal.

Optoelectronic oscillators using an optical fiber ring structure can be considered as a feedback microwave cavity. Since conventional dielectric resonators have a very short cavity length, a very high quality factor is required to ensure that the output microwave signal has a narrow linewidth and high frequency stability. Due to the limitations of size and loss, it is difficult for dielectric oscillators to achieve a large cavity length. However, after conversion to an optical signal, the wide bandwidth and low loss characteristics of optical fibers can be used to significantly reduce the longitudinal mode linewidth and make the loop more sensitive to phase, thereby achieving higher frequency stability, lower phase noise, and narrower high-performance microwave output.

Definition of a Sapphire Oscillator

Sapphire is the general term for all corundum gemstones except red, and its main component is alumina. Sapphire has extremely low dielectric loss, and its product of frequency and quality factor is the highest among all known materials. When using sapphire to build a resonator, the sapphire is usually made into a cylindrical shape and placed in a metal cavity. The support member is generally made of a low-loss, easy-to-process material. The support member connects the crystal to the metal cavity.

A sapphire oscillator (SRO) utilizes a high-Q sapphire resonator as an ultra-narrow band filter, along with amplification and phase shifting stages, to build an oscillator that generates a stable frequency after being driven by related circuits. Since the oscillation and signal output are directly realized in the X band, the deterioration of phase noise caused by the traditional frequency multiplication and filtering and amplification stages is avoided. Therefore, the frequency stability of the sapphire oscillator SRO far exceeds that of the crystal frequency multiplier at frequencies far from the carrier.

Sapphire oscillators are divided into low-temperature sapphire oscillators (CSO) and constant-temperature sapphire oscillators (SRO). CSOs typically use liquid helium or liquid nitrogen refrigeration to lower the temperature of the sapphire crystal, thereby achieving an extremely high quality factor and ultra-stable output. However, due to the expensive and bulky refrigeration equipment, the use of CSOs is limited. SROs use constant temperature control to maintain the temperature of the sapphire crystal within a certain range of room temperature, avoiding the frequency fluctuations caused by external temperature changes, so that SROs can be applied in a variety of occasions.

Difference between Optoelectronic Oscillators and Sapphire Oscillators

Optoelectronic oscillators combine the advantages of microwave technology and photonic technology, and have the advantages of large bandwidth and high frequency. They can be used as high-performance microwave photonic signal sources and applied in various occasions involving the generation, processing or reception of microwave signals.

The structure of optoelectronic oscillators is more complex, especially the need for long optical fibers, which may be several kilometers long, making them difficult to integrate and apply in engineering.

In the basic loop of a sapphire oscillator, the sapphire resonator, as the core device of the system, can be regarded as a very narrow band filter, which filters out other spurious signals, and the signal spectrum is extremely pure, and a super-stable signal can be obtained.

The sapphire oscillator has a compact structure, is easy to integrate, and can be designed to minimize the effects of temperature and vibration. It can be used as a modular structure and has good application prospects.

Compact Sapphire Oscillator

One of the constant-temperature sapphire oscillators currently on the market is the TQSRO-C50 developed and manufactured by Changsha Tianqiong Electronics. It is a compact constant-temperature sapphire oscillator that uses a high-quality factor sapphire resonator as its core component to output ultra-low phase noise signals. It uses high-precision constant temperature control to overcome the influence of external ambient temperature, and the stability of its output signal is significantly better than that of crystal frequency multipliers. It can be locked by an external reference. TQSRO-C50 has excellent performance and provides reference frequency signals for wireless telemetry, broadband communication, quantum measurement and remote