New EM750 Narrow-Linewidth Semiconductor Laser
The Gooch & Housego EM750 represents a new generation of OEM narrow-linewidth lasers. It is based on the EM650 family of integrated DFB lasers known for their ultra-low noise, stability, and tunability. The new EM750 combines these traits with a mechanism that retains all the advantages of the EM650, but reduces the linewidth to a typical value of <10 kHz.
Laser linewidth is the spread of the wavelength spectrum of a laser and a measurement of the laser spectral coherence. Linewidths in a typical laser can be of the order of 1 GHz but complex stabilized low-power continuous-wave lasers can be very narrow and reach down to less than 1 kHz. The limits are often due to noise in drive current and acoustic vibrations creating random changes of the phase of the laser emission in time. This phase noise becomes evident when phase sensitive measurements, such as with interferometers, are being made so narrow-linewidth lasers can enable very high sensitivity measurements.
There are already several types of kHz linewidth lasers commercially available including diode pumped solid state lasers, stabilized fiber lasers and external cavity diode lasers. These lasers are now starting to be used for a wide range of communication and sensing applications including coherent communication, analog RF links, laser interferometry, LIDAR wind detection, long distance fiber and fiber array sensing, acoustic and seismic monitoring. Strategies Unlimited forecast the market for narrow-line laser sources like this as $17 million in 2013.
The new EM750, based on our EM650 DFB laser, is a significant simplification in the design of a kHz laser. DFB Lasers use a diffraction grating in the active region of the semiconductor device and our EM650 DFB laser achieves 300 kHz linewidths. The EM750 stabilizes the phase noise of the EM650 with proprietary passive G&H fiber optics. The laser phase noise is significantly reduced for frequencies below ~15 MHz. Linewidths of <10 kHz are achievable sacrificing very little of the EM650 power. The first versions released are rated at 35 mW across the 1.55 micron wavelength C-Band. The phase noise reduction is not wavelength sensitive and so the EM750 can operate over the full tuning range of the DFB (~±75GHz) without compromising the linewidth, making it well suited for high-resolution laser spectroscopy.
Relative Intensity Noise (RIN) is the measure of how the output power of the laser fluctuates and is another significant measurement of the stability of a laser’s output. The EM750 RIN is also very low. In particular, and unlike all the other kHz lasers available, the RIN of the EM750 is <-140 dBc/Hz across the entire range from 10 kHz to 40 GHz, making it suitable for the most demanding analog applications.
Since the EM750 does not rely on active feedback, sensitive external cavities, or other complex opto-mechanical arrangements the design is inherently stable and highly scalable. The module is compact at 124 x 78 x 10 mm and consumes no more power than an unstabilized DFB module.
G&H believes this new laser will be the foundation for a rapidly expanding series. We have demonstrated 80 mW prototypes and expect to release a higher power version in the near future.