Optical module including a Peltier device therein and having a co-axial type package

1. Field of the Invention

The present invention relates to an optical module, in particular, a light-emitting module including a Peltier device therein and having a co-axial type package.

2. Related Prior Art

It is well known that a light-emitting module, which installs a semiconductor laser diode for the light-emitting device therein, contains a thermoelectric device, such as Peltier device, for controlling a temperature of the laser diode (hereinafter denoted by LD). In such optical module, the LD is mounted on the Peltier device, and the Peltier device, supplied by the current, controls the temperature of the LD.

However, the optical module having a package of, so called the CAN type or the co-axial type, has various subjects when installs the Peltier device therein. That is, such package, 1) extremely restricts the device mounting area generally called as a stem, 2) shows an inferior heat dissipation efficiency because paths for heat dissipation is restricted to the stem, and 3) the optical axis of the output light makes a right angle to the device mounting area that restricts the arrangement of the device installing.

According to one feature of the present invention, an optical module, comprising a laser diode (LD), a Peltier device, a block, and a photodiode, is provided. The Peltier device mounts the LD via a chip carrier thereon. The block is mounted on the Peltier device, and may include a device mounting portion and a light-reflecting portion. The LD is mounted on the device-mounting portion of the block via a chip carrier. The light-reflecting portion includes a surface for reflecting the light emitted from the LD to the photodiode. In the present invention, the photodiode is mounted outside the Peltier device.

Since the cooling efficiency of the Peltier device fully depends on the number of the bonding wire to be connected to devices mounted on the Peltier device, and the photodiode is mounted outside the Peltier device, the power consumption of the Peltier device may be reduced.

Moreover, since the block has both functions to mount the LD and to reflect light emitted from the LD, the form factor to install the reflecting member and the mounting member may be reduced. This is particularly effectual in the optical module having the co-axial type package. In the arrangement of the present invention, the optical axis of the LD, which connects the light-transmitting facet to the light-reflecting facet of the LD, is perpendicular to the optical axis of the PD.

The optical module in the present invention may further include a package having a stem and a cover. The stem, having a disk shape, mounts the Peltier device and the photodiode thereon. The stem may further include lead pin having a flat tip portion. The photodiode may be installed on the flat portion of the lead pin. Thus, the form factor to install devices may be further reduced.

The LD may be mounted on the side surface of the block such that the optical axis thereof directs to a direction perpendicular to the stem, and the optical axis of the photodiode is in parallel to the stem. Thus, the light emitted from the light-reflecting facet of the LD is reflected by the surface of the block and enters the photodiode.

FIG. 1 is a partially cutaway perspective view of an optical module according to the present invention; and

FIG. 2 is a cross sectional view taken along the ling II-II in FIG. 1 .

Next, preferred embodiments according to the present invention will be described as referring to accompanying drawings. In the drawings and their explanations, same symbols and numerals will be referred to same elements without overlapping explanations.

FIG. 1 is a perspective view partially cutaway view of the optical module 100 to show the inside thereof, and FIG. 2 is a sectional view taken along the line II-II in FIG. 1 . The optical module 100 has a package type called as a CAN-type or a co-axial type, and contains a Peltier device 10 , a block 12 , a laser diode, hereinafter denoted as LD, and a photodiode 16 in the package.

The Peltier device 10 is a thermoelectric device to control a temperature of the LD 14 . The Peltier device 10 has an upper surface 10 a and a lower surface 10 b , one of which absorbs heat and the other emits heat depending on the current supplied to the Peltier device, which enables the LD to be heated up or cooled downs.

The block 12 , which is made of electrically conductive material in this embodiment, is an optical member for mounting the LD thereon. The block 12 is mounted on the upper surface 10 a of the Peltier device. As illustrated in FIG. 2 , the block 12 includes a device-mounting portion 12 a , which is substantially quadrangular, and a light-reflecting portion 12 b having a trapezoidal cross section.

A chip carrier 19 is disposed on the side surface 12 c of the device-mounting portion 12 a , and the LD 14 is mounted on the chip carrier 19 . The LD 14 has a front facet passing through the light and a light-reflecting facet reflecting the light. A thermistor, which monitors the temperature of the LD, is disposed in the vicinity of the LD and on the chip carrier.

The light-reflecting portion 12 b of the block 12 includes a surface 12 d for reflecting light emitted from the LD 14 . The surface 12 d is inclined to both the upper surface 10 a of the Peltier device 10 and the side surface 12 c of the device-mounting portion 12 a . The light-reflecting portion 12 b may be formed by coating the surface thereof.

The Peltier device 10 is mounted on the stem 20 of the package. The stem has a disk shape and is made of iron or an alloy metal of copper and tungsten (CuW). The primary surface 20 a of the stem 20 is in contact with the lower surface 10 b of the Peltier device 10 . A plurality of lead pins 51 to 57 passes through the stem 20 . The tips of the lead pins 51 to 54 are formed in flat. Other tips 55 a and 56 a of the lead pins 55 and 56 are cylindrical. These tips 51 a to 56 a of the lead pins 51 to 56 protrude from the primary surface 20 a of the stem 20 .

The photodiode 16 monitors the magnitude of the optical output of the LD 14 . The photodiode 16 is mounted on the flat portion 53 a of the lead pin 53 , accordingly, electrically connected thereto. The photodiode 16 is mounted on the flat portion 53 a such that the light-receiving surface thereof faces to the surface 12 d of the block 12 , namely, the photodiode is disposed such that the optical axis thereof makes a right angle to that of the LD 14 . Thus mounted photodiode receives the light emitted from the LD 14 and sends an electrical signal corresponding to the magnitude of the received light to the lead pin 53 .

Between the device-mounting portion 12 a of the block 12 and the flat portion 51 a of the lead pin 51 is connected by the bonding wire 61 . Another bonding wire connects the thermistor 18 and the flat portion 52 a of the lead pin 52 . The output from the thermistor 18 is sent to the lead pin 52 via the bonding wire 62 . The photodiode 19 is connected to the stem 20 , the chip carrier 19 is connected to the lead pin 54 , and the Peltier device 10 is connected to the lead pins 55 and 56 by the bonding wire 63 , 64 , 65 and 66 , respectively. The Peltier device 10 is driven by the current supplied from the lead pins 55 and 56 via the bonding wires 65 and 66 .

The tip portions 51 a , 52 a and 54 a of respective lead pins protrude from the primary surface 20 a of the stem 20 enough length to shorten the length of bonding wires 61 , 62 and 64 to be connect to the LD 14 , the thermistor 18 and chip carrier 19 in spite of the levels of these devices from the primary surface 20 a . Moreover, since the tip portions of these lead pins 51 , 52 , and 54 are formed in flat, the wire bonding thereto may be facilitated.

A cap is provided on the stem 20 to cover the Peltier device 10 , the block 12 , the LD 14 , and the photodiode. The cap is also made of iron. On the top of the cap 26 is provided a lens 28 , which concentrates the light emitted from the LD 14 .

As illustrated in FIG. 2 , the optical axis 30 of the lens 28 coincides with that of the LD 14 . The optical axis 30 makes a right angle to the primary surface 20 a of the stem 20 and the upper surface 10 a of the Peltier device 10 . The side surface 12 c of the block 12 is in parallel to the optical axis 30 , and the surface, by which the light from the LD 14 to the photodiode 16 is reflected, is inclined by substantially 45° to the side surface 12 c , namely, to the optical axis 30 .

The light 40 emitted from the front facet 14 a of the LD 14 transmits upward along the arrow 34 , axis illustrated in FIG. 1 , in parallel to the optical, enters the lens 28 , is concentrated thereby, and outputs from the module 100 .

On the other hand, the light emitted from the rear face 14 b of the LD 14 transmits downward along the arrow 36 in parallel to the optical axis 30 , and enters the surface 12 d . Since the surface 12 d is inclined by substantially 45° to the optical axis 30 , the surface 12 d changes the direction of the light in a right angle. Therefore, the light reflected by the surface 12 d advances along the arrow 38 to the photodiode 16 . The optical axis 32 of the photodiode 16 makes a right angle to that of the LD 14 , and is parallel to the primary surface 20 a of the stem 20 and the upper surface 10 a of the Peltier device 10 . Therefore, The reflected light 42 advances in parallel to the optical axis 32 , the primary surface 20 a of the stem 20 , and the upper surface 10 a of the Peltier device 10 , and finally enters the photodiode 16 . The photodiode 16 generates the electrical signal depending on the magnitude of the received light. The signal is output to the outside via the lead pin 53 .

In the present arrangement of the optical module 100 , the power consumption thereof can be reduced, because the cooling efficiency of the Peltier device may be enhanced. Generally, almost all the power supplied to the Peltier device is consumed to the electrical-to-thermal conversion. The cooling efficiency of the Peltier device fully depends on the number of the bonding wire connected to the devices mounted thereon. The many the wire, the greater the quantity of heat conveyed from the outside to the vicinity of the LD 14 via the bonding wires, which increases the electrical power supplied to the Peltier device to cool down the devices mounted thereon. Thus, to enhance the cooling efficiency of the Peltier device, it is preferable to decrease the wires connected thereto.

In the present embodiment, the photodiode is disposed outside the Peltier device 10 , which reduces the bonding wires to be connected to the devices mounted thereon and, as a result, enhances the cooling efficiency of the Peltier device 10 . The optical module 100 can be operated in lower power consumption.

The second advantage of the present invention is to miniaturize the optical module 100 . The block 12 of the optical module 100 has both functions to mount the LD 14 and to reflect the light emitted from the LD 14 . Therefore, the form factor to install the reflecting member and the mounting member can be reduced, which is, in particular, effectual in the optical module having the CAN type or the co-axial type package.

While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be within the spirit and scope of the invention as defined by the appended claims.