BY MEGHAN FULLER
Startup Iolon Inc. (San Jose, CA) recently unveiled Apollo, a tunable external-cavity laser (ECL) that combines micro-electromechanical systems (MEMS) actuators, micro optics, and servo control to achieve the same optical performance parameters as its fixed-wavelength predecessors. Designed for long-haul, ultra-long-haul, and metro-core networks, the Apollo is tunable across the entire C-band and designed to enable carriers to provide bandwidth on demand and provision new services quickly and cost-effectively. Iolon is tapping into what appears to be a healthy market. According to industry analyst RHK Inc. (San Francisco), the market for tunable lasers will exceed $1 billion by 2004.
In response to an ever-increasing demand for bandwidth, today's carriers are lighting more wavelengths on their DWDM systems. This move to a greater number of wavelengths is creating a logistics nightmare for equipment vendors, component manufacturers, and carriers alike. Each wavelength in a DWDM system requires its own fixed-wavelength laser to produce the necessary frequency signal, and additional lasers are needed for backup and sparing-all of which adds complexity and cost to the network. Enter the tunable laser, capable of tuning across an entire range of wavelengths and designed to replace an array of fixed-wavelength devices.Despite healthy competition from the likes of New Focus's PowerTune, Princeton Optronics's PowerSweep 2000, and Agility Communications Inc.'s 3040 tunable devices, Iolon is confident that its unique design will prove a key differentiator. The company's founder, Hal Jerman, is a veteran of the MEMS industry. He was previously involved in designing MEMS for pressure sensor applications, which employ micro-mechanical pop-up mirrors that perform an actuation function and optical function on a single substrate.
Iolon's patent technology uses deep reactive ion etch (DRIE) to produce the MEMS actuators. Rather than depositing materials on a single substrate, which is how pop-up MEMS are made, Jerman and his team have developed actuators designed or etched in pure silicon. The result is an actuator that is comparatively rigid, enabling accurate and reliable movement of the optical pieces. A mirror is attached to the actuator to form the complete MEMS device.
The tuning itself occurs when a voltage is added to the MEMS actuator, which electrostatically rotates the mirror to enable a particular wavelength to couple back into the laser cavity, where it is diffracted off a high-pitch grating.
Continuous, instantaneous control is provided by an advanced servo system. Servo control "feeds position and other parameters back into the system so you can very accurately control in real-time the position of the laser," explains Eric Selvik, product-line manager for tunable lasers at Iolon. "So when you do have a vibration, it will automatically compensate for that and keep the laser locked on a wavelength."
The Apollo's design enables it to achieve key performance parameters, including output power. Today's fixed-wavelength devices achieve high output power-on the order of 10-30 mW-but can only emit light at one wavelength; they sacrifice tunability for high power. The Apollo currently achieves a minimum of 10 mW, and the company promises a 20-mW device by this summer.
Unlike other tunable devices that may suffer from varying output power, Iolon's laser features steady output power, regardless of wavelength, across the entire tuning range, claims Cindana Turkatte, Iolon's vice president of marketing. Its specification is on the order of 0.25 dB over the entire C-band.
Apollo's spectral purity is also on par with existing fixed-wavelength lasers, says the company. Its time-averaged linewidth specification is less than 10 MHz, and its instantaneous linewidth specification is on the order of 2 MHz.
Other critical performance parameters include side-mode suppression ratio (SMSR), wavelength stability, and relative intensity noise (RIN). Apollo features an SMSR of less than 50 dB, and its wavelength stability is ±1.25 GHz or 10 pm. The RIN or cleanliness of the signal is -145 dB/Hz.
While there seems to be no question about the potential for tunable lasers in the future, it remains to be seen whether the industry will embrace such devices immediately or is committed to fixed-wavelength lasers for at least the short term. Karen Liu, senior analyst at RHK, asserts that "people would gladly switch to tunable lasers if they won't have to give up any other specification as a tradeoff for tunability. They basically have nothing to lose....The definition of 'nothing to lose' includes-now that power is out of the way-price."
Iolon is banking on its background in the optical disk-drive industry to give it a slight edge in the area of cost-effectiveness. Its core team has been together for four years, originally working at Seagate on MEMS for optical disk drives like those found in CD players, the manufacture of which requires strong time-to-volume capabilities. Iolon hopes its advanced automation process-using robots to place the MEMS actuators-will result in cost reductions that they will be able to pass along to the customer.