Symmorphix Joins the Amp Camp
In integrated optics, the key issue often isn’t what you're making but how you're making it. That’s why the moment has come to roll the drums for Symmorphix Inc., another startup developing optical components based on erbium-doped waveguides.
Symmorphix has just inaugurated a pilot production facility for making such components, one that uses a totally different process technology from the other players in this market segment (see Symmorphix Touts Wafer Advance). These now include France’s Teem Photonics, Denmark’s Cisilias A/S, America’s Northstar Photonics Inc., and Australia’s Redfern Integrated Optics (see Which Amp is the Champ?).
All of these outfits are making the semiconductor equivalents of Erbium Doped-Fiber Amplifiers (EDFAs). Instead of doping fibers with erbium, they’re doping tiny waveguides in chips to make low-power amplifiers, and then combining the amps with other devices on the same piece of substrate to create a range of different components. As this process lends itself to mass production, components made in this way have a bright future in metro equipment, where cost is a crucial issue and high-power amplification isn’t necessary.
In future, Symmorphix sees the addition of embedded amplifier blocks as crucial to the development of optical integrated circuits. Even though the optical losses of individual components are coming down significantly, losses accumulate as more and more functions are integrated. "The idea is that optical integration isn't going to be limited by losses," notes Bill Lee, Symmorphix’s VP of product management and marketing.
As noted, Symmorphix's speciality is its manufacturing method. According to Lee, it's the only company using physical vapor deposition (PVD) to make waveguide amps, a technique borrowed from the flat panel display industry. All Symmorphix's founders originate from the division of Applied Materials Inc. that builds equipment for making flat panel displays.
PVD is better than other manufacturing processes in several respects, Lee contends. In the first place, it's a low temperature (below 350 degrees C) technique. High temperature is bad because it "deactivates" the erbium, resulting in lower gain from devices.
Second, PVD has been shown to have very high yields. It's used to lay down the thin-film transistors that operate the pixels in a flat panel display. Typically, at most one or two pixels will be bad across a 15-inch display.
PVD is a relatively simple method for depositing a thin layer of silica on top of a substrate. First, a solid "target" is created, which contains the materials that are to be incorporated into the thin layer. An electron beam then knocks material off the target and onto the substrate. It's basically "atomic-level sandblasting," says Lee.
The techniques employed by Symmorphix's competitors fall into two camps. Cisilias and Redfern use plasma-enhanced chemical vapor deposition (PECVD), while Northstar and Teem use ion exchange. Appreciating their good and bad points entails looking at some of the process details.
In PECVD, the materials to be deposited on the substrate are introduced as a vapor rather than a solid. Erbium doesn't exist in a gaseous state, so it's introduced in an organic compound, which gets chemically decomposed into its constituents at the substrate surface. The substrate is heated to speed up the reaction. Lee contends that even then it's quite difficult to vaporize the erbium, since out of the three approaches, this one results in the lowest erbium concentration. As a result, devices made this way need to be bigger.
Ion exchange is rather different. High temperatures allows ions, typically silver or potassium, to diffuse from the outside in to create a region of high refractive index. Since the ions possesses an electronic charge, an electric field can be used to pull them inside the bulk material (when the ion supply is turned off). But the buried waveguides are a funny shape. Read: polarization problems and difficulty in pumping the amplifier.
PVD is not without its own drawbacks, however. The equipment costs "tens of millions of dollars," according to Lee, which goes a long way towards explaining how Symmorphix has spent $13 million in venture equipment leasing (see Symmorphix Lands $13 Million).
This sum comes on top of the $28 million of equity financing that the company scored last year (see Symmorphix Scores $25M Round 1). The main investors are Battery Ventures, and Crescendo Ventures.
Symmorphix plans to kick of its product line with a 4-channel EDWA array, which it hopes to introduce in Q1 2002. To follow, it intends to integrate the pump lasers, eliminating the need for four pump laser packages, four fusion splices, and four fiber pigtails. Beyond that, designs will probably be customized, incorporating different passive components according to a customer's needs.
— Pauline Rigby, Senior Editor, Light Reading
Want to know more? This very topic is the subject of a session at Lightspeed Europe, Light Reading’s annual conference, on December 4-6, 2001, in London. For details, see: Amplifiers