晶体管激光器(transistor-laser，TL)──即一种同时具备光学与电气输出的晶体管，发明TL的工程师表示，这种器件非常适合半导体转向整合光学的趋势；但他们也指出，若是真的开始在电路中采用TL，目前的电子学教科书恐怕都得改写，因为TL颠覆了该领域存在已久的电荷守恒定律(conservation of charge)，以及基尔霍夫定律(Kirchhoff"s Law)。
美国伊利诺大学教授Milton Feng表示：“就像是晶体管对现今的IC所带来的影响，我们预期晶体管激光器也将带来类似的影响力，为光电整合IC以及光学互连开启新的视野。”Milton Feng与其同事Nick Holonyak、在读博士Han Wui Then一同发明晶体管激光器。晶体管激光器虽然已经问世约六年的时间，但其发明人却是一直到最近才为该技术与传统电路理论之间的失配(miss-match)问题找到解答。
在乔治˙欧姆(Georg Ohm)定义了电路理论中的第一个定律之后不久，古斯塔夫˙基尔霍夫(Gustav Kirchhoff)提出了迄今仍广为传授的、被称为“基尔霍夫定律”的电荷守恒原则，即：“在电路的任何一个接面，流入该节点的电流总量会与流出该节点的电流总量相同。”但在晶体管激光器中，有部份电流是要前往制造激光束──也就是混合了电荷守恒与能量守恒(energy conservation)。
因此Feng指出：“新的教科书需要把激光晶体管包含在里面，‘基尔霍夫电流定律’应该被重新定义为‘基尔霍夫电流与能量定律’。”?
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开发TL的美国伊利诺大学教授Milton Feng与Nick Holonyak
研究人员为其基于量子阱(quantum-well-based)的晶体管激光器制作了等效电路，能用以准确地建立该晶体管激光器基底(也就是激光器发光之处)的充放电机制模型。也因此，现在可以通过计算机仿真的方式来研究TL电路，进行其频率与时域(time-domain)性能的分析。研究人员并已经在一个用三五族半导体材料所制作的晶体管激光器原型上，验证了其算法。
该原型的发光层是以砷化铟镓(indium gallium arsenide)量子阱、以三明治夹层方式与p型半导体基底组合而成；其发光腔(emitting cavity)为2.2μm宽、0.85cm长，发光波长1.0μm，阈值电流40mA，能在3GHz频率对该激光进行直接调变。接下来，该研究团队计划打造可应用在IC设计的整套晶体管激光器功能区块。
参考原文：Transistor-laser breaks Kirchhoff"s Law, rewrites textbooks，by R. Colin Johnson
Transistor-laser breaks Kirchhoff"s Law, rewrites textbooks
The EE inventors of the transistor-laser (TL) —a transistor with both optical and electrical outputs—claim it fits perfectly within the semiconductor migration path to integrated optics. Unfortunately, all the electronics textbooks will have to be rewritten to use TLs in circuits, inventors say, because the transistor-laser breaks the time-worn concept of conservation of charge—Kirchhoff"s Law.
"Similar to the way the transistor impacted today"s electronic integrated circuits, we expect the transistor laser to have a similarly major impact--opening up new frontiers in electro-optical integrated circuits and for optical interconnects," said professor Milton Feng, who performed the work with fellow professor Nick Holonyak and doctoral candidate Han Wui Then.
The transistor laser has been known for about six years, but its inventors only recently crafted a solution for its miss-match with traditional circuit-theory. In particular, shortly after Georg Ohm defined the first principle of circuit theory—Ohm"s Law—Gustav Kirchhoff described the still-universally-taught conservation-of-charge principle, called Kirchhoff"s Current Law (circa 1845): "At any junction in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node." But with a transistor laser some of the current goes to creating the laser beam—mixing charge conservation with energy conservation.
"New text books will be needed to incorporate the transistor laser," said Feng. "Kirchhoff"s Current Law should be redefined as Kirchhoff "s Current and Energy Law."
The researchers have created an equivalent circuit to their quantum-well-based transistor-laser that accurately models the charging and discharging mechanisms in the transistor-laser"s base, where lasing occurs. As a consequence, TL circuits can now be studied in computer simulations that analyze both frequency and time-domain performance. The researchers have verified their algorithm on a prototype transistor-laser cast in III-V materials. The emitting layer was composed of indium gallium arsenide quantum wells sandwiched inside a p-type base. An emitting cavity of 2.2 microns wide and 0.85 millimeter long emitted at 1.0 micron wavelength, had a threshold current of 40mA and enabled direct modulation of the laser at 3 GHz.
Next the team plans to construct a set of transistor-laser building blocks for use in integrated circuit design.
Funding was provided by the U.S. Army Research Office.
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