Photonic integrated circuits - a new approach to laser technology

OPTOELECTRONICS BULLETIN OF THE POLISH ACADEMY OF SCIENCES TECHNICAL SCIENCES, Vol. 60, No. 4, 2012 DOI: 10.2478/v10175-012-0079-5 Photonic integrated circuits – a new approach to laser technology R. PIRAMIDOWICZ1∗, S. STOPIŃSKI1,2 , K. ŁAWNICZUK1,2 , K. WELIKOW1, P. SZCZEPAŃSKI1 , X.J.M. LEIJTENS2 , and M.K. SMIT2 Institute of Microelectronics and Optoelectronics, 75 Koszykowa St., 00-662 Warszawa, Poland COBRA Research Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands 1 2 Abstract. In this work a brief review on photonic integrated circuits (PICs) is presented with a specific focus on integrated lasers and amplifiers. The work presents the history of development of the integration technology in photonics and its comparison to microelectronics. The major part of the review is focused on InP-based photonic integrated circuits, with a short description of the potential of the silicon technology. A completely new way of fabrication of PICs, called generic integration technology, is presented and discussed. The basic assumption of this approach is the very same as in the case of electronic circuits and states that a limited set of standard components, both active and passive, enables designing of a complex, multifunctional PIC of every type. As a result, functionally advanced, compact, energy efficient and cost-optimized photonic devices can be fabricated. The work presents also selected examples of active PICs like multiwavelength laser sources, discretely tunable lasers, WDM transmitters, ring lasers etc. Key words: integrated optoelectronics, laser technology, photonic integrated circuits, indium phosphide. 1. Introduction It is well known that the rapid development of integrated electronics, observed in the past decades, started from very simple analog systems, consisting of a number of separate, discrete components, such as resistors, capacitors and transistors. The resulting devices occupied considerable space and were consuming high amounts of electrical power. Also the reliability was a serious problem. The situation changed with the advent and further development of monolithically integrated circuits, which revolutionized the way of thinking about electronic circuits. The next major breakthrough was the establishment of the CMOS (Complementary Metal-Oxide-Semiconductor) technology standard. Rapid progress of the CMOS capabilities enabled mass production of functionally advanced and relatively cheap electronic integrated circuits (ICs). The evolution of complexity of CMOS circuits follows Moore’s law, which states that the number of transistors on integrated circuits doubles every two years. Nowadays, chips integrating even milliards of elements are fabricated. Simultaneously, the miniaturization of electronic devices and development of integration technology enabled production of multi-functional, energy efficient, compact and portable devices, which may be effectively operated with small-size batteries. A good example is the modern cell phone with computational power far higher than early supercomputers. All these factors caused that silicon-based ICs are now ubiquitously applied in every field of technology and everyday life. A similar trend to miniaturization and integration is observed in the semiconductor photonics industry. The rapid development of semiconductor-based photonic devices started with the invention of the light emitting diode (LED) in 1955 [1] and semiconductor laser diode (LD) operating at room temperature in 1970 [2]. The operating principle of these components is based on radiative recombination of the carriers within the forward-biased p-n diode made of direct band-gap materials, which allows emission of light, amplification and/or lasing (depending on the structure and materials used). After four decades of continuous development LEDs and LDs are key elements in modern telecommunication, data storage and data processing systems, optical sensors and sensing networks, image processing systems etc. The progress in semiconductor light sources was accompanied by intensive research and development of other optical components – light modulators, detectors, low-loss waveguides, couplers and (de) multiplexers etc. At present, all of these elements are available in integrated form. It should be noted here that from the point of view of integrated solutions – the invention of the semiconductor optical amplifier (SOA) [3] was a real breakthrough, enabling both amplification of the optical signals with gain as high as 30 dB [4] and design of various types of integrated semiconductor lasers, described in the following part of this paper. Apart from impressive results obtained up to now in integrated photonics the choice of an optimal technology is still an open issue. In general, two main approaches are being developed in parallel – the first is based on silicon technologies while the second is focused on group III-V semiconductors. This work is focused on the second approach, however our intention was to provide also brief information on silicon photonics. 1.1. Silicon photonics. When considering integration of several functionalities on a single chip, the silicon platform is ∗ e-mail: 683 Unauthenticated | 89.67.242.59 Download Date | 5/19/13 8:52 PM R. Piramidowicz et al. an obvious choice, as it has already demonstrated fabrication of very large scale (electronic) integrated circuits. It is well known that the CMOS technology is mature, reliable and relatively cheap. What is more, it offers a very attractive possibility for integrating both photonic and electronic functionalities. A significant drawback of silicon, however, is its indirect band-gap which prevents effective amplification and generation of light. Despite the fact that presently it is limited to passive functionalities, the silicon technology platform for photonics has been extensively developed [5], offering high performance, good process control and low cost of fabrication for photonic integrated circuits. Another approach was proposed by Intel Corporation, as an outcome of extensive research on optical data transmission inside the computers, servers and data centers, as the traditional, copper-based solutions have been reaching the theoretical speed limits. Intel presented AlGaInAs based hybrid laser integrated on a silicon chip which consists of waveguides, amplitude modulators and an output multiplexer [6]. This solution combines the advantages of both AlGaInAs (active material) and silicon (good passive properties, low-cost and mature fabrication technology). The result is a 50 Gb/s photonic data link consisting of a hybrid-integrated transmitter and a fully-silicon receiver [7]. It should be noted that Intel achieved also laser action in silicon itself, using Raman effect and cascaded operation scheme, in which one laser line acted as the pump for the next one [8]. However, this device required an external optical pumping, therefore not suit (...truncated)