Abstract: A light emitting control apparatus comprises a light emitting element which emits a light when an input electrical signal is converted into a light signal, a monitoring circuit which monitors the output level of the light emitting element, a sample-and-hold circuit which detects a peak value and is put into the sample mode when data of the monitoring circuit is in the mark state showing voltage and which is in turn put into the hold mode when the data is in the space state showing no voltage, and an amplifier which accomplishes negative feedback control of the output level of the light emitting element by using the output of the sample-and-hold circuit. Thus, the apparatus can quickly respond to a change of the input state and stabilize the output level of the light emitting element for a long time.

Abstract: A negative feedback preamplifier having variable conversion gain control and variable open loop gain control capabilities which can work correctly regardless of semiconductor process variations. The negative feedback preamplifier used to convert an input signal current to a signal in the form of voltage includes: a resistor which determines the current-voltage conversion gain when a small signal current is input to the negative feedback preamplifier; a diode which switches the current-voltage conversion gain when a large signal current is input to the negative feedback preamplifier; a resistor which determines the current-voltage conversion gain when the large signal current is input; a grounded source amplifier including a main FET which is biased such that its transconductance decreases when the large signal current is input; and a bias setting portion (diode) which determines the bias condition associated with the main FET.

Abstract: Reflectors each having a reflectance peak wavelength within a band of the wavelength characteristics of a laser amplification factor in the unsaturated state of each light source for excitation are provided between light sources for excitation and an optical coupler, and stable wavelength locking is effected by returning a portion of a small portion of excited light reflected by the reflectors into the light sources for excited light.

Abstract: This invention provides an optical amplifier which has low noise characteristics for a wide range of input signal electric power. The optical amplifier has a plurality of cascaded optical amplifying units, a signal level detector, and a pump-source controller. The pump-source controller changes controlling objects from a pump-source corresponding to a first one of the optical amplifying units to a pump-source corresponding to a second one of the optical amplifying units according to a detection level of the signal level detector from a low level to a high level. When the detection level is outside of a control object range, the optical amplifier controls an output from the pump-source to stabilize. When the detection level is within the control object range, the optical amplifier controls an output from a pump-source of each of optical amplifying units according to the detection level.

Abstract: A light amplifying apparatus adopting a redundant structure. Optical isolators 13, 14 are inserted between pump light sources 1, 2 and a photocoupler 4 so as to prevent injection locking, thereby preventing fluctuation of pump power.In another embodiment, optical fibers 15 adequately longer than the coherence length of the excitation light waves output from the pump light sources are provided. In still another embodiment, the frequency of the driving current for the pump light sources is modulated. In a further embodiment, wave plates 20, 21 are provided so as to circularly polarize the light waves output from the pump light sources clockwise and counterclockwise.

Abstract: An optical fiber which amplifies an input signal by a pump source, a compensation-signal source which injects a compensation-signal propagating contra-directionally with respect to the input signal Into the optical fiber, a gain detector which measures a spontaneous emission light of the pump source at an input side of the optical fiber and a compensation-signal source controller which controls output of the compensation-signal source based on output of the gain detector are provided. In addition, a coupler and a wavelength selective reflector which reflects a light of the same wavelength as the compensation-signal selectively, are provided at the input side of the optical fiber.

Abstract: An optical transmission apparatus is disclosed which comprises a light emitting element for outputting an optical output in order to transmit data, a current modulation circuit, a bias current generating circuit and a resistor circuit connected in parallel with the emitting element. The current modulation circuit supplies a binary modulated current to the emitting element in response to an input binary data to the transmitted, the bias current generating circuit provides a bias current to the emitting element and the resisor circuit, whereby said bias current is kept higher than a specified level.

Abstract: A star network optical transmission system comprising a star coupler as a center node, wherein a star coupler is provided with an optical fiber exhibiting a multimode transmission characteristic to an optical signal transmitted by said star coupler at an input portion and an output portion, an optical transmission apparatus having a laser with a wavelength of .lambda. as a light source, an up optical fiber exhibiting a single mode transmission characteristic to a wavelength of .lambda. connecting the optical transmission apparatus to the star coupler, an optical reception apparatus, and a down optical fiber exhibiting a multimode transmission characteristic at a wavelength .lambda. and connecting the optical reception apparatus to said star coupler.