In recent years, together with the progress toward higher brightness of LEDs (Light Emitting Diodes), there has been an increasing demand for higher heat dissipation to the submount on which those LEDs are mounted. As an example of the submount of high heat dissipation, a submount using diamond is cited. The submount of diamond is used in optical communication systems for long distance transmission. Optical communication systems for long distance transmission, because of their relatively high prices, permit the use of higher-cost component parts such as diamond.
However, low-priced submounts are indispensable for cost reduction in the illumination or on-vehicle equipment using plural high-brightness LEDs or in the optical communication systems for long distance transmission of relatively low set prices. In these kinds of equipment or system, therefore, in order to enhance cost reduction as well as heat dissipation, it has been practiced that a face of an end-face emission type LD (Laser Diode), the face being close to its active layer, is die-bonded onto a submount of relatively low price which is formed by a chip of SiC (silicon carbide) or other ceramic or Si (silicon) chip.
In the case where a plane-emission type LED or plane-reception type PD (photodiode) is used as a light emitting/receiving device for the aforementioned equipment, there is a need for ensuring an optical path for input or output of light to or from the light emitting/receiving device in a direction perpendicular to one surface of the submount on which the light emitting/receiving device is mounted.
FIG. 9A is a sectional view showing a light guide unit including a conventional submount having a through hole (see JP 2001-59922 A). This light guide unit has a plane-emission type light-emitting device 102 mounted at an end of a light guide member 103 serving as a submount. The light emitting plane of the light-emitting device 102 faces an opening provided at one end of the light guide member 103. The opening of the light guide member 103 is a through hole formed in the light guide member 103. The through hole is formed into such a shape as to increasingly widen toward the other end of the light guide member 103 and to open at the other end of the light guide member 103. A light transmitting member 104 for transmitting light derived from the light-emitting device 102 is placed in the through hole of the light guide member 103 so as to lead the light from the other spherical-shaped end face of the light transmitting member 104 to an optical fiber 101. The surface of the through hole of the light guide member 103 reflects the light derived from the light-emitting device 102 toward the optical fiber 101, thereby the light transmission performance is enhanced.
As shown in FIG. 9B, the light guide member 103 of a conventional submount is provided with an electrode 106 at an end thereof. The light-emitting device 102 is provided with an electrode 108 on an emission surface of the light-emitting device 102. The electrode 108 is connected to the electrode 106.
However, there would be a problem of poor heat dissipation in the light-emitting device 102 when the light guide member 103 is made of a light-pervious material such as glass or light-pervious resin for enhancement of the light transmission performance. This is because thermal conductivity of the light guide member 103 is relatively low. There is also a problem that the submount becomes expensive since the light-pervious material is higher in price than Si material or the like. In the case where the light guide member 103 is formed from a metal material by metal stamping at low cost, there can be a problem that it is difficult to obtain an excellent reflecting surface, that is, excellent light transmission performance since the surface of the through hole is liable to flaws.